Obstacles Of Different Shapes Research Articles

Influence of the shape and number of obstacles on the excitation effect of dust-containing gas explosion

To investigate the excitation effects of different shapes and quantities of obstacles in dust-containing gas explosions, this study utilized an Euler-Lagrangian model. This model simulated explosions involving dust-laden gas, applying various governing equations to address the roles of coal dust at different combustion stages and its dynamic forces within the flow field. The research examined a 9.5 % gas concentration explosion with 5 g/m3 coal dust in a straight pipeline, assessing the impacts of spherical, regular tetrahedral, and cuboidal obstacles, as well as combinations of 1–3 cuboidal obstacles and three differently shaped obstacles on the explosion's flow field structure, overpressure, and flame propagation speed. Key findings include: dust-containing gas explosions result in more complex flow field structures, and the excitation effects of coal dust and obstacles on flame propagation speed exhibit mutual inhibition. Obstacles increase the maximum overpressure locally without affecting the overall trend of increasing overpressure with distance in closed conduits. Cuboidal obstacles show the most pronounced excitation effects, followed by regular tetrahedral and spherical obstacles, respectively. The number of obstacles also progressively enhances their excitation effects. When three obstacles of different shapes are present, cuboidal and regular tetrahedral obstacles primarily affect the flow field structure, with flame propagation speed and maximum explosion overpressure slightly lower compared to the presence of three cuboidal obstacles alone. These findings offer valuable insights into the destructive effects of gas explosions and the excitation effects of obstacles, providing theoretical support for disaster prevention and recommendations for underground equipment design and layout.

A compound planning algorithm considering both collision detection and obstacle avoidance for intelligent demolition robots

This paper presents a compound planning algorithm considering both collision detection and obstacle avoidance for intelligent demolition robots working safely in high-radiation environments. Firstly, configurations and kinematics of the intelligent demolition robot are detailed to detect the possible obstacles in its workspace. A collision detection function based on the improved dual vector method is proposed to detect the different distances between the robot and obstacles in three cases: a point and a line segment, two line segments, and a line segment and a geometric shape. This function can also be applied to detect collisions with various obstacles of different shapes reasonably and efficiently. Furthermore, an obstacle avoidance function based on modified gradient projection method considering multi-task transformation is proposed. According to the different distances between the robot and the obstacle, it can be used in three situations: end obstacle avoidance task, end effector operation task, and end trajectory tracking task. This function can be applied to avoid obstacles both in the workspace and on the desired path. Finally, a simulation system is established to verify the collision detection and obstacle avoidance algorithms of the intelligent demolition robot. An experiment was conducted on the intelligent demolition robot. This robot can successfully achieve the expected trajectory with the method described in this article. Results of simulation and experiment demonstrate that obstacles both in workspace and on desired path can be detected and avoided properly.

Computational investigation of magnetohydrodynamic convective flow in a trapezoidal cavity with multiple obstacles via finite element analysis

The present research deals with magnetohydrodynamic (MHD) natural convection within a trapezoidal cavity under the influence of inner solid obstacles of different shapes. The cavity includes two horizontal plates and two heated circular cylinders and is subjected to a uniform horizontal magnetic field. The walls of the domain can either be heated or cooled isothermally. The finite element method is used to solve the Oberbeck-Boussinesq equations that govern the fluid flow and heat transfer process. Three different thermal conditions are considered for the horizontal plates: isothermal heating, isothermal cooling, and adiabatic. The investigation explores the impact of varying Rayleigh numbers (Ra = 104–106), Hartmann numbers (Ha = 0–100), and thermal boundary conditions for inner horizontal plates on the flow patterns and heat transfer efficiency. The results indicate that as the Rayleigh number rises and the magnetic field strength diminishes, a noticeable improvement in heat transfer is observed, particularly in cases where the horizontal plates are subjected to cooling. Conversely, the heated inner horizontal plates exhibit less effective energy transport across the considered three configurations. It should be noted that the heat transfer rate for Ra = 106 can be increased more than 5 % when cooled ones will replace the heated inner plates. Whilst a transition between the adiabatic inner plates to cooled ones allows improving the average Nusselt number at the bottom heated wall at about 3 %. Moreover, the convective flow intensity can be described using the kinetic energy, where a growth of the magnetic field strength from 0 till 100 for Ra = 105 decreases the total kinetic energy at 76 times for heated plates, at 100 times for cooled plates and at 92 times for adiabatic plates.

A Herd-Foraging-Based Approach to Adaptive Coverage Path Planning in Dual Environments.

Coverage path planning (CPP) is essential for robotic tasks, such as environmental monitoring and terrain surveying, which require covering all surface areas of interest. As the pioneering approach to CPP, inspired by the concept of predation risk in predator-prey relations, the predator-prey CPP (PPCPP) has the benefit of adaptively covering arbitrary bent 2-D manifolds and can handle unexpected changes in an environment, such as the sudden introduction of dynamic obstacles. However, it can only work in bounded environment and cannot handle tasks in unbounded one, e.g., search and rescue tasks where the search boundary is unknown. Sometimes, robots are required to handle both bounded and unbounded environments, i.e., dual environments, such as capturing criminals in a city. Once encountering a building, the robot enters it to cover the bounded environment, then continues to cover the unbounded one when leaving the building. Therefore, the capability of swarm robots for the coverage tasks both in bounded and unbounded environments is important. In nature, herbivores live in groups to find more food and reduce the risk of predation. Especially the juvenile ones prefer to forage near the herd to protect themselves. Inspired by the foraging behavior of animals in a herd, this article proposes an online adaptive CPP approach that enables swarm robots to handle both bounded and unbounded environments without knowing the environmental information in advance, called dual-environmental herd-foraging-based CPP (DH-CPP). It's performance is evaluated in dual environments with stationary and dynamic obstacles of different shapes and quantity, and compared with three state-of-the-art approaches. Simulation results demonstrate that it is highly effective to handle dual environments.

Three-Dimensional Guidance Approach with Obstacle Avoidance against Maneuvering Targets

A guidance approach with obstacle avoidance is proposed for maneuvering target interception. Firstly, by decomposing the constrained optimal guidance problem into two associated subproblems, the overall scheme of guidance is presented. Secondly, to improve the guidance accuracy against the maneuvering target, an MPC controller with disturbance estimation is designed, which transforms the global optimization problem into a finite-horizon optimal control problem. An auxiliary controller is also developed to ensure the system’s stability. Then, to achieve obstacle avoidance without affecting the guidance accuracy, a unified function is built to assess the threats from obstacles of different shapes, based on which the optimal guidance-obstacle avoidance model is established. Finally, to solve the above optimization problems, a hybrid solver is developed based on the adaptive moment estimation (Adam) algorithm, whose output will serve as the real-time guidance command. The numerical simulation results show that the guidance approach presented in this paper can achieve precise guidance and obstacle avoidance in various scenarios, and the Monte Carlo experiment further demonstrates the robustness and computation efficiency of the approach.

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.

Influence of obstacle morphology on safety of nuclear hydrogen production system

The safety of the nuclear hydrogen production system is a key issue that cannot be ignored in the future commercialization. The reasonable arrangement of obstacles can effectively improve the safety of the system under accident conditions. In this paper, based on the high-pressure hydrogen storage tank model of a nuclear hydrogenation plant, two mechanisms by which obstacles can effectively improve safety are analyzed. In order to determine the obstacle design scheme with outstanding effect, the response surface methodology is used to study the influence of the structural parameters and spatial position parameters of obstacles of different shapes, and the comprehensive performance of different obstacles is compared by the TNO multi-energy method. The results show that the semi-cylindrical surface can control the separation distance within 141 m at a lower processing cost, which has good engineering utilization value. This study can provide a valuable reference for the design of nuclear hydrogen production systems.

Entropy Generation in 2D Lid-Driven Porous Container with the Presence of Obstacles of Different Shapes and under the Influences of Buoyancy and Lorentz Forces.

This paper includes a numerical investigation of a hybrid fluid containing 4% of Al2O3-Cu nanoparticles in a lid-driven container. The upper wall of the container has a high temperature and is movable. The lower wall is cool and wavy. An obstacle is set in the middle of the container for its effect on thermal activity. The medium is permeable to the fluid, and the entire system is immersed in a fixed-effect magnetic field. The digital simulation is achieved using the technique of Galerkin finite element (GFEM) which solves the differential equations. This investigation aims to know the pattern of heat transfer between the lateral walls and the lower wall of the container through the intervention of a set of conditions and criteria, namely: the strength of the magnetic field changes in the range of (Ha = 0 to 100); the chamber porosity varies in the range of (Da = 10−5 to 10−2); the strength of buoyancy force is varied according to the Grashof number (Gr = 102 to 104); the cross-section of the baffle includes the following shapes—elliptical, square, triangular and circular; the surface of the lower wall contains waves; and the number changes (N = 2 to 8). Through this research, it was concluded that the triangular shape of the baffle is the best in terms of thermal activity. Also, increasing the number of lower-wall waves reduces thermal activity. For example, the change in the shape of the obstacle from the elliptical to triangular raises the value of Nu number at a rate of 15.54% for Ha = 0, N = 8, and Gr = 104.

Free as a Bird: Event-Based Dynamic Sense-and-Avoid for Ornithopter Robot Flight

Autonomous flight of flapping-wing robots is a major challenge for robot perception. Most of the previous <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sense-and-avoid</i> works have studied the problem of obstacle avoidance for flapping-wing robots considering only static obstacles. This letter presents a fully onboard dynamic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sense-and-avoid</i> scheme for large-scale ornithopters using event cameras. These sensors trigger pixel information due to changes of illumination in the scene such as those produced by dynamic objects. The method performs <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">event-by-event</i> processing in low-cost hardware such as those onboard small aerial vehicles. The proposed scheme detects obstacles and evaluates possible collisions with the robot body. The onboard controller actuates over the horizontal and vertical tail deflections to execute the avoidance maneuver. The scheme is validated in both indoor and outdoor scenarios using obstacles of different shapes and sizes. To the best of the authors’ knowledge, this is the first event-based method for dynamic obstacle avoidance in a flapping-wing robot.

RRT* and Goal-Driven Variable Admittance Control for Obstacle Avoidance in Manual Guidance Applications

In manual guidance robotic applications, like the handling of large and heavy objects in a cluttered environment, it is important to guarantee that the operator accurately reaches the goal position without collisions with working isles or other obstacles in the surrounding environment. When the transported object is bulky, the operator’s view is obstructed and the situation becomes more critical. In this work, a novel variable admittance control provides the operator with a directional haptic feedback about the best motion direction towards the goal. This feedback allows the user to accurately reach the target position in a cluttered environment, also in case his/her view is partially or totally obstructed. To select the best motion direction in a cluttered workspace, a tree-based structure rooted in the goal is optimally built offline to fully explore the environment free-space based on the workspace layout and regardless of the initial position. Then, at each time instant, the optimal motion direction is determined based on the current position with respect to the exploring structure and on the user motion intention. In this work, to build the tree structure, we adapt RRT* algorithm to the manual guidance context and we define a tailored cost function. The performance is evaluated in many scenarios with a variable number of obstacles of different shapes involving several subjects and a Comau Smart Six robot.

An experimental study of oil slick contraction by chemical herders and fragmentation by obstacles

Chemical herders are a promising technique for treatment of oil spills in icy waters at high latitudes. However, obstacles on the water surface such as floating ice affects or interferes with all spill response countermeasures including chemical herder operations by fracturing the contracting oil slick and trapping small oil patches. Here we experimentally investigate the fluid dynamics of oil slick contraction and the interaction of the contracting oil slick with single obstacles of different shapes and sizes in a laboratory scale basin using Alaska North Slope crude oil and OP-40 herding agent. Oil slick area and thickness, oil-herder interface contraction speed, and the spatial distribution of the slick were optically measured over time, and particle image velocimetry (PIV) was used to measure the flow of the oil slick around the obstacles. For all obstacle sizes and shapes, an oil tail in the obstacle wake was generated as the oil-herder interface passed, which subsequently fractured by a capillary-type instability. Larger and less streamlined obstacles retained greater amounts of oil in these tails. In addition, a widely used theoretical thin film spreading model was successfully used to describe the spreading of the chemical herder against the oil slick at equilibrium. These results provide a foundation for future investigation of synergistic trapping of oil by multiple obstacles as would be seen in the field.

An improved ant colony algorithm for integrating global path planning and local obstacle avoidance for mobile robot in dynamic environment.

To improve the path optimization effect and search efficiency of ant colony optimization (ACO), an improved ant colony algorithm is proposed. A collar path is generated based on the known environmental information to avoid the blindness search at early planning. The effect of the ending point and the turning point is introduced to improve the heuristic information for high search efficiency. The adaptive adjustment of the pheromone intensity value is introduced to optimize the pheromone updating strategy. A variety of control strategies for updating the parameters are given to balance the convergence and global search ability. Then, the improved obstacle avoidance strategies are proposed for dynamic obstacles of different shapes and motion states, which overcome the shortcomings of existing obstacle avoidance strategies. Compared with other improved algorithms in different simulation environments, the results show that the algorithm in this paper is more effective and robust in complicated and large environments. On the other hand, the comparison with other obstacle avoidance strategies in a dynamic environment shows that the strategies designed in this paper have higher path quality after local obstacle avoidance, lower requirements for sensor performance, and higher safety.

Escape Path Obstacle-Based Mobility Model (EPOM) for Campus Delay-Tolerant Network

In Delay-Tolerant Networks (DTNs), humans are the main carriers of mobile devices, signifying that human mobility can be exploited by extracting nodes’ interests, social behavior, and spatiotemporal features for the performance evaluation of DTNs protocols. This paper presents a new mobility model that describes students’ daily activities in a campus environment. Unlike the conventional random walk models, which use a free space environment, our model includes a collision-avoidance technique that generates an escape path upon encountering obstacles of different shapes and sizes that obstruct pedestrian movement. We evaluate the model’s usefulness by comparing the distributions of its synthetic traces with realistic traces in terms of spatial, temporal, and connectivity features of human mobility. Similarly, we analyze the concept of dynamic movement clusters observed on the location-based trajectories of the studied real traces. The model synthetically generates traces with the distribution of the intercluster travel distance, intracluster travel distance, direction of movement, contact duration, intercontact time, and pause time similar to the distribution of real traces.

A Comparative Study of Optimization Algorithms for Global Path Planning of Mobile Robots

It is an essential issue for mobile robots to reach the target points with optimum cost which can be minimum duration or minimum fuel, depending on the problem. In this paper, it was aimed to develop a software for the optimal path planning of mobile robots in user-defined two-dimensional environments with static obstacles and to analyze the performance of some optimization algorithms for this problem using this software. The developed software is designed to create obstacles of different shapes and sizes in the work area and to find the shortest path for the robot using the selected optimization algorithm. Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC) and Genetic Algorithm (GA) were implemented in the software. These algorithms have been tested for optimum path planning in four models with different problem sizes and different difficulty levels. When the results are evaluated, it is observed that the ABC algorithm gives better results than other algorithms in terms of the shortest distance. With this study, the use of optimization algorithms in real-time path planning of land mobile robots or unmanned aerial vehicles can be simulated.

Numerical investigation of convective heat transfer in fluid flow past a tandem of triangular and square cylinders in channel

A numerical study of a two-dimensional laminar flow and heat transfer characteristics in a horizontal channel containing two in-line obstacles of different shapes, namely an upstream triangular cylinder and a downstream square cylinder, was carried out. It is based on a coupling between the Lattice Boltzmann Method (LBM) and the Finite Difference Method (FDM). The airflow (Pr = 0.71) is assumed to be laminar and incompressible. All physical properties of the fluid, expect its density, are supposed to be constant. The two cylinders are kept at a constant hot temperature, while the incoming flow is at a cold temperature. The Reynolds number and the horizontal separation distance between the cylinders are varied to investigate their influences on fluid flow and heat transfer.

Numerical study of heat generating γ Al2O3– H2O nanofluid inside a square cavity with multiple obstacles of different shapes

A numerical research on uniformly heat generating γ Al2O3–H2O nanofluid filled square cavity with multiple obstacles of different shapes is carried out. The cavity is assumed to be heated at bottom and cooled by vertical walls with linearly varying temperature. An adiabatic condition is assumed at the top of the cavity. Circular, square and triangular shaped obstacles are considered. The mathematical model has been solved using Galerkin finite element method. Results are presented for streamlines, isotherms, local and mean Nusselt numbers. Multiple rotating cells are observed in the streamlines. It is found that the local and mean Nusselt numbers increase with nanoparticle volume fraction and higher heat transfer is achieved in the cavity with triangular obstacles.

Flame acceleration and deflagration-to-detonation transition in hydrogen-air mixture in a channel with an array of obstacles of different shapes

Numerical simulations were conducted to study the flame acceleration and deflagration-to-detonation transition (DDT) in a channel with a bank of aligned obstacles. The multidimensional, fully compressible reactive Navier–Stokes equations coupled to a calibrated chemical-diffusion model for stoichiometric hydrogen-air mixture were solved using a high-order numerical algorithm. The results in the case with circular obstacles show that occurrence of DDT arises from shock focusing at flame front. Higher blockage ratio leads to faster flame acceleration and facilitates the formation of choked flame. Heat losses can significantly attenuate flame acceleration and delay detonation initiation in case of DDT, and even hinder occurrence of DDT for high blockage ratio. To understand the effect of shape of obstacle on the flame acceleration and DDT, circular, square, left triangular, and right triangular shapes, always maintaining the same formal blockage ratio, were simulated. The simulations indicate that there are significant differences in flame acceleration and DDT among these differently shaped obstacles, although the basic mechanism for detonation initiation is similar in all of the cases studied and involves interactions of shock wave with flame front and reactivity gradient. Square obstacles produce the largest growth rate of flame surface area in the flame-acceleration stage and thus result in the fastest flame acceleration and shortest detonation onset time compared to circular or triangular obstacles. Circular obstacles produce the weakest flame-surface growth, and thus they have the least effect on promoting flame acceleration and transition to detonation. A closer analysis shows that the sharp angles of the triangular obstacles, when compared to the circular obstacles, are more conducive to flame stretching and convolution and thus facilitate flame acceleration and DDT. The results also show that the effect of obstacle shape does not correlate with obstacle area.

Pore-scale simulation of gas flow in microscopic permeable media with complex geometries

Lattice Boltzmann method (LBM) is an efficient tool to perform direct numerical simulation of gas flow in micro-size pores. Despite great advances in LBM and its use in describing gas flow in micro-size channels in slip and transitional flow regimes, exploring formulations that are able to capture flow behavior in domains with complex boundary geometries remains a challenging task. As a result, the impact of complexities in pore structures on gas flow may not be fully explored using LBM. In this study, we propose to use the combined bounce-back and Maxwellian diffusive reflection scheme to capture the slip velocity with a new set of slip coefficients. Optimal values of slip coefficients are determined using a gradient based method, where the results from the linearized Boltzmann equation is used as the reference solution. The proposed formulation is further validated against predictions from molecular dynamics simulation in the presence of complex geometries by introducing obstacles of different shapes in straight channels. LBM with the proposed boundary treatment is then used to investigate gas flow in a synthetic microscopic permeable medium. Results indicate that gas exhibits different flow configurations as Knudsen number varies, and apparent gas permeability appears to have up to a second-order dependency on the reciprocal mean pressure in slip and transitional flow regimes.

Boundary condition control of fluvial obstacle mark formation – framework from a geoscientific perspective

ABSTRACTObstacle marks are sedimentary bedforms, typically composed of an upstream local scour hole and a downstream sediment accumulation in the vicinity of an obstruction that is exposed to a current. However, specific morphologies are variable in fluvial, coastal and submarine environments. Although obstacle marks and the phenomenon of local scouring are subject to different scientific disciplines, the objectives of investigations are rather incoherent and no systematic framework for analysing and evaluating boundary condition control exists yet, especially concerning limited knowledge of the cause and effect relationship of obstacle mark formation at instream boulders or vegetation elements in variable environmental conditions. Thus, a parameter framework is developed which identifies a spectrum of extrinsic and intrinsic boundary conditions that control the major process dynamics of obstacle mark formation. The framework is composed of dimensionless control parameters that are separated by a hierarchical order regarding their significance for obstacle mark formation. Primary control parameters determine the geometrical scale of flow field at the obstacle, and therefore control the potential maximum size of the obstacle. Secondary control parameters affect the dynamics of the flow field in geometrical scale and limit the potential maximum size of the emerging sedimentary structure if thresholds are crossed. The framework is supposed to be a foundation for subsequent quantification and determination of thresholds by systematic laboratory studies. To elucidate this, flume‐based research is presented, evaluating the influence of different flow levels at boulder‐like obstacles of different shapes. The results show that obstacle mark dimensions were maximized at shallow flow depths compared to obstacle dimensions, while deep flows at submerged boulder‐like obstructions caused considerably smaller obstacle marks. In interdependency with a rounded and more streamlined obstacle shape, deep flows even cause a deviation of morphology if the flow depth above an obstacle exceeds 1.6 times the obstacle's dimensions. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.

The Effect of Flow Obstacles of Different Shapes for Generating Turbulent Flow for Improved Performance of the Solar Air Heater

It is common knowledge that by creating turbulent aspect of flow the efficacy of a solar collector which generally tends to have lower conversion efficiencies could be improved. An important focus for many researchers who are working keenly to improve the efficacy of conversion is by using turbulators of different configurations on the absorber plate itself. However, there is a simple method to improve the conversion efficiency by creating turbulence of the main flow by designing flow obstacles of various geometries, as discussed in this paper. These obstacles create flow turbulence such that they are able to create a better momentum exchange among the air particles. This will result in a higher enthalpy rise among the heated air particles. In this paper, an improved turbulence intensity is produced as consequence of the flow disturbance around the obstacles that causes better convective heat transfer. Flow obstacles of different shapes are studied corresponding to various geometries and under different mass flow rate considerations so as to prescribe an improved design for the solar collector.