Obstacle Placement Research Articles

Contact Risk Assessment in Dynamic Indoor Settings through Agent‐Based Modeling: A Spatially Explicit and Reproducible Approach

This study introduces an agent‐based model (ABM) pedestrian simulation tool to assess the risk of close contact (6 feet) in dynamic indoor environments, specifically in urban settings with diverse social activities and spatial structures. Our approach uses machine learning‐based sensitivity analysis (SA) to identify factors impacting the number of individual contacts, such as individual stay time and area. In addition, we conducted an in‐depth quantitative analysis to evaluate how specific factors, such as the strategic placement of obstacles, dwell time, and stay time near the entrances, mitigate the number of contacts. This analysis provides valuable insights for developing practical guidelines to curb contact risks in indoor environments. Lastly, we share the model, validation methods, and associated data as an open‐source Python library, complete with comprehensive documentation. This aims at fostering collaborative research and enables the application of our model across various scenarios, contributing to the development of spatially explicit models. Such efforts enhance the understanding of contact risks in urban indoor settings and promote joint research efforts, thus advancing the field through shared knowledge and tools.

Effect of composition gradient on detonation initiation in fuel-rich hydrogen-air mixtures in an obstructed channel

Numerical simulations were performed to study the effect of composition gradient and obstacle arrangement on detonation initiation in fuel-rich hydrogen-air mixtures. A third-order WENO method with adaptive mesh refinement (AMR) was used to solve the unsteady, fully-compressible, reactive Navier-Stokes equations coupled to a calibrated chemical-diffusive model (CDM). An obstructed channel at a blockage ratio of 0.3 filled with non-uniform hydrogen-air mixtures of an average H2 concentration 50 vol% was considered. The results show that unilateral obstacle arrangement is more conducive to flame acceleration (FA) and DDT than bilateral obstacle arrangement for both homogeneous and inhomogeneous mixtures. For inhomogeneous mixtures, the flame accelerates faster, and the detonation onset time is shorter when obstacles are placed on the sidewall with a hydrogen concentration closer to the stoichiometric ratio than the those when obstacles are placed on the other sidewall. However, the placement of unilateral obstacles on either the upper or lower sidewall does not significantly affect the DDT run-up distance. Besides, for fuel-rich inhomogeneous hydrogen-air mixtures, detonation tends to be initiated in the regions of high H2 concentration. Idealized models were introduced to simplify the intricate interactions of the reaction waves and flow fields to better understand the connection between H2 concentration distribution and detonation initiation. The analysis suggests that the minimum shock strength required for detonation initiation decreases with increasing equivalence ratio. This is supported by a kinetics analysis with detailed reaction model, which shows that ignition delay increases with decreasing equivalence ratio when detonation is about to be initiated.

Deployment of a UAV swarm-based LiFi network in the obstacle-ridden environment: algorithms of finding the path for UAV placement

The subject of this study is unmanned aerial vehicle (UAV)-based wireless networks in an obstacle-ridden environment. The aim of this study is to develop methods and software to ensure reliable LiFi communication using swarm UAVs in an obstacle-ridden environment. The objectives are as follows: 1) to describe the problem of providing a reliable UAV swarm-based LiFi network, requirements for the composition and use of UAVs, and assumptions; 2) to develop the methodology for solving research tasks; 3) to develop the method and algorithms for solving the problem, considering the requirements, assumptions, and practical limitations; 4) to explore the algorithms by developing software for modeling and searching for rational UAV placement to ensure the required UAV-based LiFi network characteristics; 5) to provide experiments and illustrative examples of the developed tool’s application. The following results were obtained. 1) The requirements for the composition and use of UAVs for creating LiFi networks, as well as assumptions and limitations for the methodology development and research task solving. 2) An obstacle avoidance method using the left and right angles algorithm. 3) A method for obstacle avoidance using the controlled waterfall algorithm. 4) A software tool for modeling and searching for rational UAV placement to ensure the required LiFi network characteristics. The tool allows route construction under obstacles in 2D space and a comparison of the developed algorithms for various variants of obstacle placement. Conclusions. The main contribution of this research is a set of methods, algorithms, and software tools for providing communications between two points using LiFi technologies and a swarm of UAVs supporting these communications as transmitters in conditions of mechanical obstacles.

Development of the Mobile Vision Enhancement System (MOVES) for Sight-Assist Mechanism

Vision-related diseases can have various effects on the human eye, ranging from minor sight distractions to the most severe cases of total blindness. There are multiple medical treatments available for the patient, as well as alternative methods, including wearable tools, to assist the patient in their daily routine activities. The most commonly used tool is the guide stick, which requires the user to hold it, thus limiting its flexibility. The technology-aided system also depends on the power supply, which also adds to the limitation. Inspired by the solar-based system, this project applies the portable sight-assist system, which is easy to use and comes with wearable design ideas. The proposed Mobile Vision Enhancement System (MOVES) is a solar-powered system that assists the user in detecting obstacles in their path. It is designed to fit in the hat worn by the user. The MOVES is designed using the Arduino Nano Microcontroller Board with a compatible poly-crystalline solar panel for solar-powered systems, an ultrasonic sensor for obstacle detection, and a buzzer for the alert system. The main objectives of the headwear design are that the system operates by using a solar panel, which is practical to place at the top, and the user does not have to hold it by hand, making it a hands-free system. The MOVES system has been tested in controlled environments with various obstacle placements. This is important, as the system must be able to detect any obstacle in the user’s pathway to avoid collisions and endanger the user. Based on the test, the MOVES had proven to be useful in assisting the user in detecting obstacles and helping the user in avoiding any obstacle in their path, with a mean relative error of less than 5%. Thus, MOVES is proposed as an alternative sight-assist system to be used by a visually impaired person.

Advanced numerical analysis of convective rarefied flows in microchannels: Studying the impact of multiple obstacle arrangements through LBM modeling

The investigation of fluid flow and forced convective heat transfer in microchannels with square barriers is the focus of this study. The positioning of obstacles was varied in three cases: at the top wall, bottom wall, and symmetrically distributed on both sides of the microchannel wall. The thermal Lattice Boltzmann Method in conjunction with the Double Distribution Function and Bhatnagar–Gross–Krook approach was used for simulation through computer code in Python. Slip velocity and temperature jump were considered in the boundary conditions for the walls of the microchannel and obstacles. The results demonstrate that the rarefaction effect, placement of barriers, and choice of square obstacles significantly impact fluid flow and heat transfer. An increase in Knudsen numbers (Kn) leads to a decrease in temperature and velocity. The presence of obstructions on both sides of the microchannel walls reduces the fluid’s velocity and cools the fluid at the microchannel’s exit. The third case, with obstacles on both sides, presents a practical approach for reducing the fluid’s temperature at the exit, resulting in the lowest level of skin friction (Cf) and a reduction in the Nusselt number (Nu). The proposed configurations can be utilized to enhance the geometry of microchannels and for cooling purposes in small-scale devices and systems with miniature mechanical and electrical components. The study’s findings suggest that the placement of obstacles at the bottom or on both sides, depending on the need for best cooling on both sides or only at the top to reduce material consumption, can achieve low temperature at the exit of a rectangular microchannel.

Investigating the Performance of the Multi-Lobed Leaf-Shaped Oscillatory Obstacles in Micromixers Using Bulk Acoustic Waves (BAW): Mixing and Chemical Reaction

Proper mixing in microfluidic devices has been a concern since the early development stages. Acoustic micromixers (active micromixers) attract significant attention due to their high efficiency and ease of implementation. Finding the optimal geometries, structures, and characteristics of acoustic micromixers is still a challenging issue. In this study, we considered leaf-shaped obstacle(s) having a multi-lobed structure as the oscillatory part(s) of acoustic micromixers in a Y-junction microchannel. Four different types of leaf-shaped oscillatory obstacles, including 1, 2, 3, and 4-lobed structures, were defined, and their mixing performance for two fluid streams was evaluated numerically. The geometrical parameters of the leaf-shaped obstacle(s), including the number of lobes, lobes’ length, lobes’ inside angle, and lobes’ pitch angle, were analyzed, and their optimum operational values were discovered. Additionally, the effects of the placement of oscillatory obstacles in three configurations, i.e., at the junction center, on the side walls, and both, on the mixing performance were evaluated. It was found that by increasing the number and length of lobes, the mixing efficiency improved. Furthermore, the effect of the operational parameters, such as inlet velocity, frequency, and intensity of acoustic waves, was examined on mixing efficiency. Meanwhile, the occurrence of a bimolecular reaction in the microchannel was analyzed at different reaction rates. It was proven that the reaction rate has a prominent effect at higher inlet velocities.

Indoor Radio Map Construction via Ray Tracing With RGB-D Sensor-Based 3D Reconstruction: Concept and Experiments in WLAN Systems

This paper proposes an RGB-D sensor-aided ray-tracing simulation framework for indoor radio map construction that models indoor information, such as walls and obstacles, as a set of cuboids. Radio maps can accelerate indoor wireless systems, including resource optimization and fingerprint-based localization. We can construct an accurate radio map using a ray-tracing algorithm with precise information about indoor structures and obstacles. However, it is difficult to acquire this indoor information because manual observations, including the placement of obstacles, are expensive. To mitigate this critical drawback, we propose the acquisition of colored point clouds using an RGB-D sensor. After the point clouds are labeled via a three-dimensional semantic segmentation task, we model the indoor information as a set of cuboids that can be immediately used for the ray-tracing simulation. Indoor experiments using wireless LANs over 5180 and 2452 MHz clarified that the proposed method accurately automates the radio-map construction process from indoor information acquisition to radio propagation simulation.

The processes of firebrand deposition and accumulation from wind‐driven firebrand showers

AbstractFirebrands, or smoldering and/or flaming particles, are in fact the main culprit to destroy structures in large outdoor fires. A recent comprehensive review of firebrand combustion reported that deposition and subsequent accumulation processes remain largely unexplored. As part of this work, a series of experiments were undertaken to investigate firebrand deposition and accumulation processes in the National Research Institute of Fire and Disaster (NRIFD)'s wind facility. A reduced‐scale firebrand generator was utilized, and various flow obstructions were placed downstream of these firebrand generators to better understand these complex deposition processes. Results of these investigations for multiple wind speeds, firebrand size and mass distributions, and obstacle placement are presented and discussed.

Emergency evacuation dynamics in complex configurations

Despite the fact that proper placement of obstacles can reduce evacuation time has been reproduced in numerous studies, there is relatively rare research on how to arrange multiple obstacles in multi-exit rooms to facilitate evacuation efficiency of pedestrians. In this letter, we investigate how the number of obstacles and their layout in a complex configuration influence evacuation time using the improved social force model. Results show that compared with one obstacle, placing two obstacles in front of the exits takes full advantage of evacuation space, thereby substantially reducing total evacuation time, especially for high pedestrian density combined with large desired velocity. We find that appropriate layout of two obstacles does not only help to remove the bottleneck near the exits, but also controls the pedestrian speed to achieve the best global evacuation efficiency. However, when obstacles are placed asymmetrically, inappropriate offset parameter may seriously hinder the evolution of evacuation dynamics.

Paraxial Propagation Properties of Symmetric Dual Pearcey Gaussian Beams in Free Space

AbstractIn this article, a new kind of symmetric dual Pearcey Gaussian beam (SDPGB) is introduced and their properties of auto‐focusing, self‐similarity, inversion, and self‐healing are discussed. The self‐similarity, the auto‐focusing, and the inversion properties of the propagating SDPGBs are turned out by analytical derivation and experimental observation. Additonally, a second‐order chirp factor for SDPGBs is introduced to investigate their secondary auto‐focusing and abrupt auto‐focusing properties in further detail. Finally, the effects of the obstacle diameter and the obstacle placement plane on the self‐healing of the SDPGBs are discussed.

Combined grid and heat conduction optimization for staircase cleaning robot path planning

Staircase climbing, particularly in complex environments of multi-storey buildings, is a challenging task for robotics. By leveraging the similarities between robot path planning and heat conduction, this paper presents a novel path planning to direct with optimal energy consumption the self-reconfigurable staircase cleaning robot called sTetro, able to transform its shape to perform both descent and ascent motions on the staircase. Finding optimal path is modeled as heat traveling between heat source and heat sink through thermal conductive materials. We utilize the temperature gradient on grid-based optimization method to search for optimal paths by minimizing path length and energy consumption. The proposed path planning method successfully applies to six virtual environments with various obstacle placements. Additionally, validation tests on a real sTetro robot in 2 real staircase scenarios show that the energy consumption of the optimized paths from the proposed method is about 21% lower than that from conventional methods.

On the Placement of an Obstacle so as to Optimize the Dirichlet Heat Content

We prove that among all doubly connected domains of R^n (n>=2) bounded by two spheres of given radii, the Dirichlet heat content at any fixed time achieves its minimum when the spheres are concentric. This is shown to be a special case of a more general theorem concerning the optimal placement of a convex obstacle inside some larger domain so as to maximize or minimize the Dirichlet heat content.

Collision avoidance and path planning for industrial manipulator using slice-based heuristic fast marching tree

With the emergence of Industry 4.0 , high productivity is critically dependent on robot manipulators . However, building an efficient and safe work environment with robot manipulators remains a challenge of hardware capability. The optimal path planning of the robot manipulator usually encounters shortcomings in low computational speed and tedious training after changing assembly lines and increases the risk during human–robot collaboration (HRC). To solve such a problem, we propose a path planning, named slice-based heuristic fast marching tree, based on joint space to achieve real-time path planning speed without modeling or training the workspace in advance. Our experimental results indicate that the time consumed for path planning in static environments is only from 0.51 s to 1.63 s, tested by a 6-DOF general-purpose industrial manipulator and different cylindrical obstacle placements. The time for path replanning in dynamic environments is from 0.62 s to 0.88 s. • Path planning is in 1.63 s with static obstacles and 0.88 s with dynamic obstacles. • The proposed path planning is faster, smoother, and shorter than RRT, RRT*, and FMT*. • The joint angles of revolutions in total are less than RRT, RRT*, FMT*.

Energy Efficient Local Path Planning Algorithm Based on Predictive Artificial Potential Field

Energy efficiency is one of the most important parameters in transportation electrification. It allows to improve the production rate due to longer operation without charging or decrease the cost related to transportation. To provide collision-free operation in unknown or various environment, the local path planning algorithm should be considered. An Artificial Potential Field (APF) algorithm is commonly used for this task, however it provides unsmooth and oscillating motion of autonomous ground vehicle (AGV), and is prone to being trapped in a local minimum, e.g, dead-end. In such a case, the energy used to achieve the goal position is higher than necessary. In this paper, the energy-efficient local path planning algorithm is proposed. Future movement prediction has been introduced to APF to allow AGV to bypass obstacles in advance. A novel method for local minimum avoidance is introduced. It is based on placement of virtual obstacles called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">top quarks</i> in critical areas. These obstacles provide additional repulsive force for the APF based path planner. Considering the predicted stagnation-free path of the AGV, the new temporary goal for APF is selected. Such a combination allows to reduce traveled route length, improve its smoothness, and bypass local minima. The proposed Predictive Artificial Potential Field (PAPF) algorithm has been examined using Husarion ROSbot 2.0 PRO mobile robot, and the obtained results in form of videos are also attached as supplementary files. In comparison to original APF, the proposed path planning algorithm allows to reduce the used electric power by 21.4 %. PAPF provided a shorter path by up to 8.73 % and shorter time to reach the goal position by up to 40.23 %. The movement of the AGV is also much smoother in a case of usage of the proposed algorithm, and the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">top quarks</i> -based local minimum avoidance mechanism allows to bypass the local minima.

Crowd Emergency Evacuation Simulation Time Analysis via Obstacle Optimization Strategy

The crowd evacuation simulation is essential to provide important results for occupants, especially in the large capacity building compared to the human fire drill exercise. The strategy of evacuation such as the use of obstacles may need to be adapted by many organizations as an aid to help in visualizing and estimating the evacuation time during an emergency. During certain crowd events, they may consider the various setting of the object to ensure smoothness and effective crowd evacuation flow. In this paper, it aims to provide the simulation with 100-1000 agents and testing with obstacle using Anylogic tool and analysis of evacuation time validated using SPSS. The results show that the placement of obstacles near the exit way indeed can reduce the evacuation time and complies with the anti-arching phenomenon during evacuation.

Pedestrian lane formation and its influence on egress efficiency in the presence of an obstacle

Due to the inevitability of placing obstacles when designing walking facilities, it is important to understand the influence of the obstacle during pedestrian egress to build a safer and more efficient walking environment. However, previous experimental studies on the influence of the obstacle during egress tend to be controversial: some suggest improving egress efficiency, whereas others do not. This controversy is probably due to the diversified obstacle layouts and pedestrian pushing degree, making the influencing mechanism of the obstacle layout alone dubious. In this paper, we focus on the obstacle layout and explore its influencing mechanism on pedestrian egress efficiency under conditions without intentional physical pushing. Controlled experiments were conducted under various obstacle layouts in terms of obstacle size and obstacle-exit distance. The preliminary analysis revealed that the obstacle layout affected egress efficiency, which we hypothesized was due to the pedestrian lane formation, i.e., the single-files of self-organized pedestrians directed toward the exit. For a quantitative validation, we proposed a novel two-layer k-means clustering method to recognize the pedestrian lanes that are nearly parallel. Accordingly, the deviation parameter, which represented the deviation of pedestrians from the established lane, was proposed to evaluate the lane-formation status. We also found a positive correlation between the deviation parameter and the egress time, suggesting that worse lane-formation status could lead to lower egress efficiency. Moreover, the deterioration of the lane-formation status was mainly caused by the lane-changing behavior, which indicated pedestrian movements from one lane to another. Further analysis showed that the lane-changing behavior was presumably motivated by the tendency of pedestrians to pursue better egress direction before the exit. Results indicated that the obstacle can be used to adjust the pedestrian lane-formation status, thus controlling the egress efficiency. We would also suggest the possibility of stabilizing the egress efficiency through restraining the pedestrian lane-changing behavior. We expect this paper to contribute to the reasonable placement of obstacles in actual walking facilities with diversified obstacle layouts and pedestrian characteristics.

Analysis of the Impact of Decreasing the Width of Direct Stairs in Apartments on RSET for All Occupants in Korea

This study analyzed the RSETs for 11-story or less apartments where the building-related laws were not retroactively applied, with consideration of the decrease of direct stairs width due to obstacles piled up on the direct stairs. The RSET was shown to be 631.8 seconds when the width of the direct stairs was 1,260mm. The evacuation time exceeded 5 minutes even when there were no obstacles due to the delayed evacuation start time. The risk increased when the width of the direct stairs was decreased to 960mm, 760mm, and 560mm because of obstacles, and the RSETs were 768.8 seconds, 803.3 seconds, and 834.4 seconds respectively. There are various ways to eliminate the occurrence of obstacles on direct stairs which increase RSET : First, it is necessary to remove the exception that permits the placement of obstacles on the stairs. Second, penalties for the placement of obstacles on the direct stairs should be enforced as written. Third, the fire safety managers need the authority to act on behalf of the fire officials. Lastly, it is necessary to encourage residents to report instances of obstacle accumulation. Henceforth, more research is needed on the spread speed of smoke and toxic gases depending on whether fire doors are installed through fire simulation.

Visual Servoing Corresponding to Various Obstacle Placements and Target Object Shapes Based on Learning in Virtual Environments

Visual Servoing Corresponding to Various Obstacle Placements and Target Object Shapes Based on Learning in Virtual Environments

What Is Economic Globalization Without Trans-boundary Migration?

The world is often regarded as a global village or borderless globe where various countries freely interconnect and interrelate towards achieving a global goal. Globalization has occasioned international cooperation amongst States through the formation of several treaties and international organizations with economic objectives. This article evaluates the law and attitude of States and International organizations towards economically motivated trans-boundary migration. Particular reference is made to World Trade Organization(WTO), European Union(EU), African Union (AU), Economic Community of West African States (ECOWAS) and North American Free Trade Association(NAFTA). Findings reveal that the legal and institutional frameworks in support of trans-boundary economic migration are very weak, thereby allowing States’ interest to prevail over the globalization objectives. State practices are geared towards placement of several obstacles, such as imposing criminal sanctions, which limits trans-boundary economic migration. This prejudice is more obvious when the trade in service is a South-North movement of labour. These challenges have led to the irresistible conclusion that economic globalization is but a political fiction yet to take root in reality. It is further contended that, the puzzle of economic globalization cannot be completely fixed, except States fully embrace, accepte and liberalize the missing piece of trans-boundary migration. Globalization, Trans-boundary migration, Economic migration, South-North movement, Trade liberalization.

Augmented LiDAR Simulator for Autonomous Driving

In Autonomous Driving (AD), detection and tracking of obstacles on the roads is a critical task. Deep-learning based methods using annotated LiDAR data have been the most widely adopted approach for this. Unfortunately, annotating 3D point cloud is a very challenging, time- and money-consuming task. In this paper, we propose a novel LiDAR simulator that augments real point cloud with synthetic obstacles (e.g., cars, pedestrians, and other movable objects). Unlike previous simulators that entirely rely on CG models and game engines, our augmented simulator bypasses the requirement to create high-fidelity background CAD models. Instead, we can simply deploy a vehicle with a LiDAR scanner to sweep the street of interests to obtain the background point cloud, based on which annotated point cloud can be automatically generated. This unique "scan-and-simulate" capability makes our approach scalable and practical, ready for large-scale industrial applications. In this paper, we describe our simulator in detail, in particular the placement of obstacles that is critical for performance enhancement. We show that detectors with our simulated LiDAR point cloud alone can perform comparably (within two percentage points) with these trained with real data. Mixing real and simulated data can achieve over 95% accuracy.