Obstacles Of Various Shapes Research Articles

Quad-Rotor Avoidance Trajectory Generation for Convex Polyhedron Obstacles

This study investigates a method for generating obstacle avoidance trajectories for arbitrary convex polyhedrons. We propose a formulation that converts discrete conditions into continuous equation forms to avoid convex polyhedron obstacles. The condition that the evaluation point be located outside of the convex polyhedron can be transformed into a constraint in the continuous equation form and incorporated into the optimization calculation to generate avoidance trajectories. Avoidance trajectory generation using the Legendre pseudospectral method is performed for convex polyhedral obstacles of various shapes. The results show that the proposed method successfully generates avoidance trajectories for arbitrary convex polyhedral obstacles.

Smart insect-computer hybrid robots empowered with enhanced obstacle avoidance capabilities using onboard monocular camera

Insect-computer hybrid robots are receiving increasing attention as a potential alternative to small artificial robots due to their superior locomotion capabilities and low manufacturing costs. Controlling insect-computer hybrid robots to travel through terrain littered with complex obstacles of various shapes and sizes is still challenging. While insects can inherently deal with certain obstacles by using their antennae to detect and avoid obstacles, this ability is limited and can be interfered with by control signals when performing navigation tasks, ultimately leading to the robot being trapped in a specific place and having difficulty escaping. Hybrid robots need to add additional sensors to provide accurate perception and early warning of the external environment to avoid obstacles before getting trapped, ensuring smooth navigation tasks in rough terrain. However, due to insects’ tiny size and limited load capacity, hybrid robots are very limited in the sensors they can carry. A monocular camera is suitable for insect-computer hybrid robots because of its small size, low power consumption, and robust information acquisition capabilities. This paper proposes a navigation algorithm with an integrated obstacle avoidance module using a monocular camera for the insect-computer hybrid robot. The monocular cameras equipped with a monocular depth estimation algorithm based on deep learning can produce depth maps of environmental obstacles. The navigation algorithm generates control commands that can drive the hybrid robot away from obstacles according to the distribution of obstacle distances in the depth map. To ensure the performance of the monocular depth estimation model when applied to insect-computer hybrid robotics scenarios, we collected the first dataset from the viewpoint of a small robot for model training. In addition, we propose a simple but effective depth map processing method to obtain obstacle avoidance commands based on the weighted sum method. The success rate of the navigation experiment is significantly improved from 6.7% to 73.3%. Experimental results show that our navigation algorithm can detect obstacles in advance and guide the hybrid robots to avoid them before they get trapped.

CFD simulations of MHD effects on mixed convectional flow in a lid-driven square cavity with square cylinder using Casson fluid

Enclosure design significantly impacts thermal engineering processes and devices, including electronic devices, thermal exchangers, power engines, heating systems, solar panels, and nuclear power plants. The square cavity with variable aspect ratios is utilized for multi-objective optimization and improved thermal performance of microchannels. Cold cylinders in square enclosures are often utilized to reduce energy loss in micro heat sinks and heat exchangers. So, article’s main objective is to investigate concurrent characteristics of external and internal forces on a Casson fluid contained in a square cavity with magnetohydrodynamics (MHD). A square cylinder is embedded in the middle of the enclosure, and an inclined magnetic field with angle φ is applied. The upper lid is assumed to be inertially driven by a constant amount of slipping velocity, and a thermal state is disturbed by assuming uniform temperature at the left wall while the right wall and embedded cylinder are cool. The finite element method (FEM) based open-source software renowned as COMSOL Multiphysics is utilized to solve the non-dimensionalized momentum and energy equations. This study uses the square enclosure to study essential factors, such as the Casson parameter β , Hartmann number Ha , Reynolds number Re , and Grashof number Gr . The findings reveal that the kinetic energy at β = 10 is 12.22 times greater than that of β = 0.1 at Ha = 0 . It is observed that Ha , β , and Gr have a direct impact on the local Nusselt number. Fluid kinetic energy increases as Gr increases while it decreases as Re increases. This study shows how obstacles of various shapes and temperature conditions have an essential impact on handling heat transfer characteristics.

OPTIMIZATION OF MICRO HEAT SINK WITH REPETITIVE PATTERN OF OBSTACLES FOR ELECTRONIC COOLING APPLICATIONS

Micro heat sinks (MHS) are becoming integral part of microelectronics nowadays because of their ability to cool the tiny components which generate high heat flux. In this study, an electronic chip with a high heat flux of 100 W/cm<sup>2</sup> is cooled with the help of an MHS device which has repetitive patterns of obstacles of various shapes in the flow of cooling medium. Numerical modelling of all MHSs were performed using a computational fluid dynamics (CFD) solver and the pattern, which gives better thermohydraulic performance, was selected for optimization. A parametric study was performed with various obstacle sizes, distances between obstacles, and flow rates of cooling medium for maximum temperature of chip and pressure drop. Regression analysis was carried out with response surface method (RSM) between these three design variables and two objective functions, viz. thermal resistance (R<sub>th</sub>) and pumping power (P<sub>p</sub>). A multi-objective optimization of the MHS was performed using genetic algorithm (GA) and Pareto-optimal solutions were obtained. An optimal design was fabricated and the cooling experiment was carried out under optimal flow conditions. The repetitive pattern of obstacles increases the conjugate heat transfer area and helps in improving thermal performance.

Path Planning for Autonomous Systems Design: A Focus Genetic Algorithm for Complex Environments

Abstract Path planning has been a hot research topic in robotics and is a vital functionality for autonomous systems. As the time complexity of traditional path planning algorithms grows rapidly with the complexity of the problem, evolutionary algorithms are widely applied for their near-optimal solutions. However, evolutionary algorithms can be trapped in a local optimum or converge to infeasible solutions, especially for large search spaces. As the problem scale increases, evolutionary algorithms often cannot find feasible solutions with random exploration, making it extremely challenging to solve long-range path-planning problems in environments with obstacles of various shapes and sizes. For long-range path planning of an autonomous ship, the current downsampling map approach may result in the disappearance of rivers and make the problem unsolvable. This paper introduces a novel area-based collision assessment method for genetic algorithm (GA) that can always converge to feasible solutions with various waypoints in large-scale and obstacle-filled environments. Waypoint-based crossover and mutation operators are developed to allow GA to modify the length of the solution during planning. To avoid the premature problem of GA, the mutation process is replaced by a self-improving process to let the algorithm focus the operations on any potential solutions before discarding them in the selection process. The case studies show that the proposed GA-focus algorithm converges faster than RRT* and can be applied to various large-scale and challenging problems filled with obstacles of different shapes and sizes, and find high-quality solutions.

The phenomenon of a swirling gas flow transformation when it passes through a cellular structure

The distribution of the gas mixture swirling turbulent flows at the flow around obstacles of various shapes in the inter-machine channel of the developed ventilation system without pipes is studied. The conducted studies confirmed the effectiveness of the proposed spatial system at the development of ventilation without pipes or ship and industrial premises of complex configuration. Keywords swirling air flow, crowded placement, flat and cylindrical obstacle, acoustic characteristics, noise and pressure reduction, Reynolds number, gas mixtures, intensification, heat and mass transfer, Pesochinskiy plan

РАЗРАБОТКА МНОГОУРОВНЕВОЙ СИСТЕМЫ ПЛАНИРОВАНИЯ ТРАЕКТОРИИ ДВИЖЕНИЯ ГРУППЫ АНПА В НЕИЗВЕСТНОЙ СРЕДЕ С ПРЕПЯТСТВИЯМИ

The article discusses the problem of organizing the group movement of marine robotics(MRS), in particular, unmanned autonomous underwater vehicles (AUV), in an a priori unknownenvironment with obstacles. A brief analysis of existing projects on the subject of MRS group control,and path-planning algorithms have been carried out. The presence of numerous studies inthis area confirms the relevance of the indicated problem. The formal statement of the problem ofthe movement of four robots in formation is presented. The proposed method for a group pathplanning is based on a combined approach that organizes a multi-level solution to organizing themovement of MRS. At the upper level, a system for global path planning and mission control wasdeveloped based on the random tree method, which provides the general movement of the groupbased on a priori information about the state of the environment. The lower-level planning systemadjusts the global path, allowing objects at the local level to carry out the group agents’ movementand interaction, including ensuring their collision-free movement in environment and exit from theareas of local minima. The article provides a detailed analytical description of the developed algorithmand a block diagram of its functioning. Numerical simulation of the movement of a groupof 4 AUVs in a non-deterministic environment with fixed obstacles is carried out. The simulationwas carried out taking into account obstacles of various shapes and complexity. The results ofmathematical modeling demonstrated the solution to the problem of the exit of the AUV groupfrom the area of the local minimum. Full-scale tests are presented on the example of a group ofthree unmanned boats: a group of mobile objects formed a formation and carried out a movementin a given formation to target positions and returned to the final zone. In addition, the local planningmodule developed within the framework of this article was integrated into the software of the"Shadow" underwater glider control system. In the conclusion, the results of the proposed methodand its further development, in particular, its application in 3D environment, are considered.

Система обходу навчальних перешкод безпілотним повітряним судном

The problem of creating a system for simulating the flight of an unmanned aircraft or remotely piloted aircraft system between buildings is solved, which uses multi-mode flight control by dividing the trajectory of the unmanned aircraft into several sections. The boundaries of each section are presented in the form of additional intermediate points of the route. The developed system is used to visualize the flight of an unmanned aircraft. The problem statement for the system of bypassing polygonal obstacles is formulated. The simulation of the training flight trajectory of a remotely piloted aircraft system or unmanned aircraft between two specified destinations with the avoidance of obstacles of different sizes is considered, taking into account that the number of movements in real time should be minimized. An algorithm for controlling the flight of an unmanned aircraft along a given trajectory from one point to another has been developed. It is proposed to divide the given trajectory into several smaller parts and determine the boundaries of these newly created parts in the form of coordinates of destinations. An algorithm and a block diagram of the algorithm for bypassing obstacles of different sizes have been developed. Simulations are performed and experimental results are given. The proposed method is designed to implement movement on a given trajectory with a given speed and power required to transmit information. The simulation results show the effectiveness of the algorithm for modeling the flight path, its re-planning when detecting obstacles of various shapes.

Design and analysis of a potential-based controller for safe robot navigation in unknown GPS-denied environments with strictly convex obstacles

Abstract In this paper, we propose an obstacle avoidance controller for a disk-shaped holonomic robot with double-integrator dynamics and local sensing. The control objective is for the robot to converge to a target velocity while avoiding collisions with strictly convex obstacles in an unbounded environment. We assume that the robot has no information about the location and geometry of the obstacles, has no localization capabilities, and can only measure its own velocity and its relative position vector to the closest point on any obstacles in its sensing range. We first propose a potential-based controller for the case with a single obstacle, and we prove that the robot safely navigates past the obstacle and attains the desired velocity. For the case with multiple obstacles, we propose a switching control scheme in which the robot applies the single-obstacle controller for the closest obstacle at each instant. We investigate the correctness of this switching control law and demonstrate the absence of local stable equilibrium points that would trap the robot. We validate our analytical results through simulations of a robot that uses the proposed controllers to successfully navigate through an environment with strictly convex obstacles of various shapes and sizes.

Identification of obstacles immersed in a stationary Oseen fluid via boundary measurements

In this paper we consider the interior inverse problem of identifying a rigid boundary of an annular infinitely long cylinder within which there is a stationary Oseen viscous fluid, by measuring various quantities such as the fluid velocity, fluid traction (stress force) and/or the pressure gradient on portions of the outer accessible boundary of the annular geometry. The inverse problems are nonlinear with respect to the variable polar radius parameterizing the unknown star-shaped obstacle. Although for the type of boundary data that we are considering the obstacle can be uniquely identified based on the principle of analytic continuation, its reconstruction is still unstable with respect to small errors in the measured data. In order to deal with this instability, the nonlinear Tikhonov regularization is employed. Obstacles of various shapes are numerically reconstructed using the method of fundamental solutions for approximating the fluid velocity and pressure combined with the MATLAB toolbox routine lsqnonlin for minimizing the nonlinear Tikhonov's regularization functional subject to simple bounds on the variables.

Anomalous tracer diffusion in the presence of extended obstacles on a triangular lattice

Proteins diffuse to their sites of action within cells in a crowded, strongly interacting environment of nucleic acids and other macromolecules. An interesting question is how the highly crowded environment of biological cells affects the dynamic properties of passively diffusing particles. The Lorentz model is a generic model covering many of the aspects of transport in a heterogeneous environment. We investigate biologically relevant situations of immobile obstacles of various shapes and sizes. The Monte Carlo simulations for the diffusion of a tracer particle are carried out on a two-dimensional triangular lattice. Obstacles are represented by non-overlapping lattice shapes that are randomly placed on the lattice. Our simulation results indicate that the mean-square displacement displays anomalous transport for all obstacle shapes, which extends to infinite times at the corresponding percolation thresholds. In the vicinity of this critical density the diffusion coefficient vanishes according to a power law, with the same conductivity exponent for all obstacle shapes. At the fixed density of obstacles, we observe that the diffusion coefficient is higher for the smaller obstacles if the object size is defined as the highest projection of the object on one of the six directions on the triangular lattice. The dynamic exponent, which describes the anomalous transport at the critical density, is the same for all the obstacle shapes. Here we show that the values of critical exponents estimated for all disordered environments do not depend on the microscopic details of the present model, such as obstacle shape, and agree with the predicted values for the underlying percolation problem. We also provide the evidence for a divergent non-Gaussian parameter close to the percolation transition for all obstacle shapes.

Experimental Analysis of a Plume Dispersion Around Obstacles

Nowadays, transport and deposition of aerosol particles (PM2.5, PM10, TSP) caused by industrial plants, environmental applications and transports, are of great concern to public health. Despite the establishment by the European Union of emission standards (European directive 2008/50/CE e.g) to control the limits of particulates in the air, the emissions by industrial plants are still not accurately monitored. In particular, the interaction between plume dispersion and obstacles, such as buildings, is not currently well studied. A lot of theoretical researches were carried out in this field with a lack of experimental data comparison. This paper focuses on a laboratory work made to better explain the interaction of a continuous plume released from a point source and various obstacles. First of all a vertical pipe was reproduced, a continuous aerosol emitter was characterized in terms of a specified and controlled mass flow and the ratio between smoke emission and the total suspended particulates thanks to use of the certified gravimetric calculation of PM10. The experimental campaigns were conducted by means of a wind tunnel all the data collected were validated. The characterization of plume was made by the use of several sensors and calculation of velocity in several points of the field. Moreover, the plume dispersion was studied also by using digital image analysis. It was then investigated downwind the influence of obstacles of various shapes and distances from source in terms of aerosol concentration in several points.

Calculating the Fickian diffusivity for a lattice-based random walk with agents and obstacles of different shapes and sizes

Random walk models are often used to interpret experimental observations of the motion of biological cells and molecules. A key aim in applying a random walk model to mimic an in vitro experiment is to estimate the Fickian diffusivity (or Fickian diffusion coefficient), D. However, many in vivo experiments are complicated by the fact that the motion of cells and molecules is hindered by the presence of obstacles. Crowded transport processes have been modeled using repeated stochastic simulations in which a motile agent undergoes a random walk on a lattice that is populated by immobile obstacles. Early studies considered the most straightforward case in which the motile agent and the obstacles are the same size. More recent studies considered stochastic random walk simulations describing the motion of an agent through an environment populated by obstacles of different shapes and sizes. Here, we build on previous simulation studies by analyzing a general class of lattice-based random walk models with agents and obstacles of various shapes and sizes. Our analysis provides exact calculations of the Fickian diffusivity, allowing us to draw conclusions about the role of the size, shape and density of the obstacles, as well as examining the role of the size and shape of the motile agent. Since our analysis is exact, we calculate D directly without the need for random walk simulations. In summary, we find that the shape, size and density of obstacles has a major influence on the exact Fickian diffusivity. Furthermore, our results indicate that the difference in diffusivity for symmetric and asymmetric obstacles is significant.

Fluid-flow features in a plane channel of variable cross section with high clutter for obstacles of various shapes

Fluid-flow features in a plane channel of variable cross section with high clutter for obstacles of various shapes

Mesoscopic model for filament orientation in growing actin networks: the role of obstacle geometry

Propulsion by growing actin networks is a universal mechanism used in many different biological systems, ranging from the sheet-like lamellipodium of crawling animal cells to the actin comet tails induced by certain bacteria and viruses in order to move within their host cells. Although the core molecular machinery for actin network growth is well preserved in all of these cases, the geometry of the propelled obstacle varies considerably. During recent years, filament orientation distribution has emerged as an important observable characterizing the structure and dynamical state of the growing network. Here we derive several continuum equations for the orientation distribution of filaments growing behind stiff obstacles of various shapes and validate the predicted steady state orientation patterns by stochastic computer simulations based on discrete filaments. We use an ordinary differential equation approach to demonstrate that for flat obstacles of finite size, two fundamentally different orientation patterns peaked at either ±35° or +70°/0°/ − 70° exhibit mutually exclusive stability, in agreement with earlier results for flat obstacles of very large lateral extension. We calculate and validate phase diagrams as a function of model parameters and show how this approach can be extended to obstacles with piecewise straight contours. For curved obstacles, we arrive at a partial differential equation in the continuum limit, which again is in good agreement with the computer simulations. In all cases, we can identify the same two fundamentally different orientation patterns, but only within an appropriate reference frame, which is adjusted to the local orientation of the obstacle contour. Our results suggest that two fundamentally different network architectures compete with each other in growing actin networks, irrespective of obstacle geometry, and clarify how simulated and electron tomography data have to be analyzed for non-flat obstacle geometries.

Measured and Simulated Motion of a Hopping Rotochute

A new hybrid micro vehicle called the hopping rotochute has been developed to robustly explore rough and complex terrain. Unlike other jumping robots, the vehicle traverses an area by intermittently powering a small coaxial rotor system that allows the device to hop over obstacles of various shapes and sizes. A movable internal mass controls the vehicle's direction of travel, and the exterior shape and low mass center allow the vehicle to passively reorient itself to an upright attitude when in contact with the ground. This paper presents a dynamic model of the hopping rotochute used to assess the basic flight performance of the vehicle. The experimental methods used to estimate model parameters are described and comparisons between measured and simulated motion are presented. Basic flight performance predicted by dynamic simulation is reported, including maneuverability, jumping performance, and total range. The simulated results indicate that the hopping rotochute is capable of surmounting larger obstacles than current hoppers while being able to navigate with the use of a movable internal mass.

Diffusion in Cytoplasm: Effects of Excluded Volume Due to Internal Membranes and Cytoskeletal Structures

The intricate geometry of cytoskeletal networks and internal membranes causes the space available for diffusion in cytoplasm to be convoluted, thereby affecting macromolecule diffusivity. We present a first systematic computational study of this effect by approximating intracellular structures as mixtures of random overlapping obstacles of various shapes. Effective diffusion coefficients are computed using a fast homogenization technique. It is found that a simple two-parameter power law provides a remarkably accurate description of effective diffusion over the entire range of volume fractions and for any given composition of structures. This universality allows for fast computation of diffusion coefficients, once the obstacle shapes and volume fractions are specified. We demonstrate that the excluded volume effect alone can account for a four-to-sixfold reduction in diffusive transport in cells, relative to diffusion in vitro. The study lays the foundation for an accurate coarse-grain formulation that would account for cytoplasm heterogeneity on a micron scale and binding of tracers to intracellular structures.

THE COUPLED NATURAL BOUNDARY-FINITE ELEMENT METHOD FOR SOLVING THE ACOUSTIC SCATTERING PROBLEM IN A 3D OCEANIC WAVEGUIDE

This study is concerned with the problem of acoustic scattering by a three-dimensional obstacle in a shallow water waveguide. A method coupling of the finite-element and natural boundary-element is analyzed and presented for solving the acoustic scattering problem numerically based on the Galerkin variational principle and the DtN mapping theory. The proposed method has the advantage of avoiding the absorbing boundary condition of the conventional finite-element method. Numerical examples are given of successful computational results for several 3D obstacles of various shapes.

Formation of coherent structures at interaction between an impact jet and a flow reflected from an obstacle

The results of experimental research on interaction between an axisymmetric underexpanded jet and obstacles of various shapes (the plane one and in the form of a cylindrical cavity) are presented. It is found that a cavity provides formation of a reverse flow, whose interaction with a jet causes formation of the vortex spiral structures.

Radiative transfer equation for multiple diffraction

This paper aims to apply the radiative transfer method to acoustical diffraction by obstacles. Some fictitious sources are introduced at diffracting wedges and a transfer equation based on energy balance determines the diffracted powers. It leads to a set of linear equations on diffracted powers which can be solved in a finite number of steps. It is then possible to calculate the diffracted field anywhere. Some applications to diffraction by obstacles of various shapes are presented. Results of this method are compared with Geometrical Theory of Diffraction and BEM reference calculations. It is shown that this method is particularly efficient in case of multiple diffraction where the ray-tracing technique involves an infinite number of rays between a source and a receiver point.