Obstacle Size Research Articles

Effect of obstacle depth and height on step-over behavior: Focus on age-related changes.

Obstacle avoidance during locomotion is a crucial motor skill, especially in environments with uneven terrain. However, the combined effects of obstacle dimensions and aging on this ability remain unclear. This study aimed to investigate whether the action of stepping over an obstacle changes proportionally with obstacle size and how these movements evolve with age. We recruited fourteen young participants and fourteen older participants. Participants were instructed to step over an obstacle placed five meters away under nine different conditions with varying obstacle dimensions. The smallest obstacle had dimensions of 5cm×5cm (height × depth), and both height and depth were increased by 5cm increments to reach the largest obstacle size of 15cm×15cm, resulting in three levels each of depth and height conditions. An analysis of variance on the leading-foot clearance revealed significant interactions between height and depth, demonstrating a height-dependent depth effect on clearance, independent of age. Furthermore, significant interactions between height and age were observed for the heel-obstacle distance, which refers to the landing position after stepping over the obstacle. This indicates that older adults consistently landed closer to the same position at each obstacle height, whereas the landing positions of young adults moved farther away as the obstacle height increased. Our findings suggest that although both young and older adults can immediately scale the dimensions of the obstacle and consistently adjust their leading-foot movement accordingly, the landing movements of older adults follow an inflexible strategy that could potentially be riskier.

Radiation and heat generation effect on MHD natural convection in hybrid nanofluid-filled inclined wavy porous cavity incorporating a cross-shaped obstacle

Purpose This paper aims to explore, through a numerical study, buoyant convective phenomena in a porous cavity containing a hybrid nanofluid, taking into account the local thermal nonequilibrium (LTNE) approach. The cavity contains a solid block in the shape of a cross (+). It will be helpful to develop and optimize the thermal systems with intricate geometries under LTNE conditions for a variety of applications. Design/methodology/approach To attain the objective, the system governing partial differential equations (PDEs), expressed as functions of the current function and temperature, and are solved numerically by the finite difference approach. The authors carefully examine the heat transfer rates and dynamics of the micropolar hybrid nanofluid by presenting fluid flow contours, isotherms of the liquid and solid phases, as well as contours of streamlines, isotherms and concentration of the fluid. Key parameters analyzed include heated length (B = 0.1–0.5), porosity (ε = 0.1–0.9), heat absorption/generation (Q = 0–8), length wave (λ = 1–3) and the interphase heat transfer coefficient (H* = 0.05–10). The equations specific to the flow of a micropolar fluid are converted into classical Navier–Stokes equations by increasing the porosity and pore size. Findings The results showed that the shape, strength and position of the fluid circulation are dictated by the size of the inner obstacle (B) as well as the effective length of the heating wall. The lower value of obstruction size, as well as heating wall length, leads to a higher rate of heat transfer. Heat transfer is much higher for the higher amount of heat absorption instead of heat generation (Q). The higher porosity values lead to lesser fluid resistance, which leads to a superior heat transfer from the hot source to the cold walls. The surface waviness of 4 leads to superior heat transfer related to any other waviness. Research limitations/implications This work can be further investigated by looking at thermal performance in the existence of various-shaped obstructions, curvature effects, orientations, boundary conditions and other variables. Numerical simulations or experimental studies in different multiphysical contexts can be used to achieve this. Practical implications Many technical fields, including heat exchanging unit, crystallization processes, microelectronic units, energy storage processes, mixing devices, food processing, air conditioning systems and many more, can benefit from the geometric configurations investigated in this study. Originality/value This work numerically explores the behavior of micropolar nanofluids (a mixture of copper, aluminum oxide and water) within a porous inclined enclosure with corrugated walls, containing a solid insert in the shape of a cross in the center, under the oriented magnetic field, by applying the nonlocal thermal equilibrium model. It analyzes in detail the heat transfer rates and dynamics of the micropolar nanoliquid by presenting the flow patterns, the temperature of liquid and solid phases, as well as the variations in the flow, thermal and concentration fields of the fluid.

Numerical investigation of trihybrid nanofluid heat transfer in a cavity with a hot baffle

Trihybrid nanofluids, which combine the benefits of three distinct types of nanoparticles, have significant potential to enhance heat transfer in various thermal management applications. Understanding their behaviour in confined geometries with complex boundary conditions, such as a free surface and heated obstacle, is important to optimize their performance. This study investigates the heat transfer characteristics of a Cu-Al2O3-MWCNT-oil trihybrid nanofluid within a square cavity featuring a hot baffle and a free surface. Using numerical simulations and Patankar's blocked-off region method, a parametric study was conducted, varying the Rayleigh number (5000–50,000), nanoparticle volume fraction Φ (0–0.06), obstacle size and aspect ratio (h:w from 0.7 to 9), and Marangoni number (−10,000 to 10,000). The results reveal that negative Marangoni (Ma) numbers enhance convective heat transfer due to the synergistic interaction between the thermocapillary and buoyancy forces. Conversely, positive Marangoni numbers hinder heat transfer owing to competition between these forces. With increasing Rayleigh number (Ra), heat transfer enhancements of up to 45 %, 18 % with nanoparticle addition, and 22 % with varying obstacle sizes were observed. Therefore, these parameters can be varied to optimize the thermal design.

Two-dimensional distribution experiment of ‘lattice diffraction’ using ultrasound in an educational laboratory

Abstract A device that can study the two-dimensional distribution of ultrasonic diffraction on lattice structures was developed for educational laboratories, enabling students to design the size, shape and dimension of diffraction obstacles independently. In this experiment, metal balls were used to simulate atomic lattice structures, and the two-dimensional diffraction distribution data of simple cubic, body-centered cubic, and hexagonal close-packed structure were collected. The results were compared with the sound field simulation of COMSOL, and a good consistency was found. By observing the diffraction results of complex structures, students can gain a better understanding of the concept of diffraction.

Improved artificial potential field method based on robot local path information

The artificial potential field (APF) is an important method for robot path planning. However, some information in APF is not fully utilized in practical applications. In this paper, an improved artificial potential field (IAPF) method is presented, in which the local path information is defined and used. And the calculation formulas for various forces in IAPF are given, which include repulsive force (R-force) of obstacle on the robot, the attractive force (A-force) of target on the robot, and the resultant force of R-force and A-force. Then, based on the local path information, a method for solving the robot falling into local optimality problem is proposed and used into IAPF. Finally, IAPF is respectively simulated and discussed in general scenario, complex scenario, and scenarios with the same and different size of circular obstacles. The results show that IAPF has higher efficiency than traditional artificial potential field (TAPF) method and can overcome the local optimality problem. At the same time, IAPF is compared with dynamic window method in the scenarios with the same and different size of circular obstacles. The results show that IAPF is more efficient than the dynamic window approach (DWA) for robot path planning.

The coupled-motion enhanced wireless signal transmission with long distance based on Maxwell’s displacement current

Wireless signal transmission plays an increasingly imperative role in numerous aspects of modern society, but it still remains challenging to achieve it with low-cost and efficient way. Herein, we demonstrate a long-distance wireless signal transmission system, which mainly includes an electrodeless triboelectric nanogenerator coupled with linear motion and rotational motion (LR-TENG) as a transmitter and a receiver located at a distance. Based on the varying electric field originated from Maxwell's displacement current, the maximum transmission distance of LR-TENG can reach 86 cm under the external excitation of 1 Hz, creating the highest record among the relevant researches. In addition, the influence of obstacle type, thickness, size and position on signal transmission has been systematically investigated for the first time, and the distribution of time-varying electric field in space is also analyzed qualitatively. Furthermore, a Labview interface is developed for accurate positioning in complex scenes relying on the received signals from multiple receivers at different positions. This work illustrates a simple and feasible design method for extending the distance of wireless signal transmission based on TENG, and promotes its application in the field of wireless communication.

Vision-based planting position selection system for an unmanned reforestation machine

Abstract Research on automated seedling planting systems in forestry is a crucial aspect of forestry automation. This paper introduces the development of a vision-based automated seedling planting position selection system, integrated with hardware and software components on an unmanned forest machine platform. Developed around object detection as the core, this research presents a comprehensive system consisting of two main functionalities: (i) A vision system that performs obstacle detection and localization, providing estimated obstacle types, sizes, and positions to the plant planner function. (ii) A plant planner function utilizes this information to plan the plantable areas and selects suitable planting locations. The integrated system has been tested in the field and we found it to effectively determine suitable planting locations on the ground of a clear-cut. The implementation of this system lays the foundation for subsequent automated planting operations. Furthermore, the automation of forest seedling planting reduces the need for manual labor and enhances planting precision, contributing to improved forest health and ecological balance. Looking ahead, this research offers insights into the future development of unmanned forestry operations, making strides in automating forest management, achieving cost-effectiveness, and facilitating ecological restoration.

ITS4Tsunamis: An Intelligent Transportation System for tsunami emergencies

Natural disasters, such as tsunamis and earthquakes, may affect gravely on human lives, infrastructure, and economy. Negative effects of these situations can be minimized with the help of technology. In this paper we propose ITS4Tsunamis, an Intelligent Transportation System (ITS) that combines different technologies to help emergency management agencies to provide safe routes for their emergency vehicles. In the case of a tsunami emergency, these agencies must consider different aspects when moving with their vehicles, such as the road state and the vehicle features. Technologies such as Complex Event Processing (CEP) can be used to gather and process the information provided by a collection of sensors and assess the corresponding emergency level. In addition, we introduce uncertainty as a key element when determining the road-status, since this factor is uncertain by itself, and is based on the flood level and the number and size of obstacles in the roads. Fuzzy Logic (FL) is then used to deal with uncertainty and help authorities to evaluate the road accessibility. Safe routes are obtained using Colored Petri Nets (CPNs), a graphical formalism that allows us to analyze concurrent systems. This approach has been applied to Cádiz, a city in the southwest of Spain, which is close to an active tectonic rift. This work is an extended version of the conference paper by Díaz et al. (2023) [1].

Active nematic ratchet in asymmetric obstacle arrays.

We numerically investigate the effect of an asymmetric periodic obstacle array in a two-dimensional active nematic. We find that activity in conjunction with the asymmetry leads to a ratchet effect or unidirectional flow of the fluid along the asymmetry direction. The directional flow is still present even in the active turbulent phase when the gap between obstacles is sufficiently small. We demonstrate that the dynamics of the topological defects transition from flow mirroring to smectic-like as the gap between obstacles is made smaller, and explain this transition in terms of the pinning of negative winding number defects between obstacles. This also leads to a nonmonotonic ratchet effect magnitude as a function of obstacle size, so that there is an optimal obstacle size for ratcheting at fixed activity.

Stress and alignment response to curved obstacles in growing bacterial monolayers.

Monolayers of growing bacteria, confined within channel geometries, exhibit self-organization into a highly aligned laminar state along the axis of the channel. Although this phenomenon has been observed in experiments and simulations under various boundary conditions, the underlying physical mechanism driving this alignment remains unclear. In this study, we conduct simulations of growing bacteria in two-dimensional channel geometries perturbed by fixed obstacles, either circular or arc shaped, placed at the channel's center. Our findings reveal that even sizable obstacles cause only short-ranged disruptions to the baseline laminar state. These disruptions arise from a competition between local planar anchoring and bulk laminar alignment. At smaller obstacle sizes, bulk alignment fully dominates, while at larger sizes planar anchoring induces increasing local disruptions. Furthermore, our analysis indicates that the resulting configurations of the bacterial system display a striking resemblance to the arrangement of hard-rod smectic liquid crystals around circular obstacles. This suggests that modeling hard-rod bacterial monolayers as smectic, rather than nematic, liquid crystals may yield successful outcomes. The insights gained from our study contribute to the expanding body of research on bacterial growth in channels. Our work provides perspectives on the stability of the laminar state and extends our understanding to encompass more intricate confinement schemes.

Experimental study on individual and crowd movement features around obstacles with different shape and size

Well-structured pedestrian experiments in a long corridor have been carried out to explore the influence of obstacle shape and size on individual and crowd level pedestrian movement characteristics. Results indicate that for individual pedestrians, the number of right-turning pedestrians and the target drift angle show clear changes with the increase of the obstacle size, while the speed only changes significantly when the obstacle size is greater than 1.5 m. For the crowd movement scenarios, a small obstacle can speed up the pedestrian flow, then, with the increase of the obstacle size, the movement time increases. The increase rate has a relation with the obstacle shape. The obstacle shape influence becomes more obvious when the individual and crowd movement scenarios are compared. The results of this paper are expected to provide practical basis for modeling pedestrian under the influence of obstacle.

Experimental study of extinguishing shielded fires by a low-pressure multi-orifice water mist nozzle

The performance of a water mist system to suppress shielded fires is analyzed experimentally in this work. The diesel pool fire is used as the fire source in an enclosure with 2.4 m × 2.4 m × 3.1 m measurements, and a mechanism is designed to provide different shielding conditions by changing the obstacle size and height. The characteristics of a low-pressure multi-orifice nozzle including the drop diameter and the velocity are studied by a Phase Doppler Particle Analyzer (PDPA) system. In total, 10 cases with diverse shielding conditions are defined and different parameters including the temperature distribution, the gas concentrations, and the extinguishing time are measured. Based on the present data, mist droplets in some shielded fire scenarios were able to bypass the obstacle, overcome the fire plume thrust, and suppress the fire. In fire scenarios with the same obstruction size, the reduction of the distance between the obstacle and the nozzle led to an increased block ratio and consequently, the extinguishing time was decreased. It was found that the temperatures in the central axis above the fire and the lateral temperatures declined quickly in cases with short suppression time.

Vortex core regions of nebkhas and their implications on shadow dune formation

Shadow dunes develop at the lee side of obstacles and are scale-dependent on the obstacle size. However, our recent field investigations showed that the lengths of shadow dunes are not always proportional to the size of obstacles. In this work, field investigations and computational fluid dynamics (CFD) simulations were conducted to study the effects of the scale and vortex of nebkhas on shadow dune development. Results show that although the shadow dune lengths are proportionate to the width (W) and height (H) of nebkhas, the increment rate decreased massively when the W and H of nebkhas are larger than 6 and 2 m, respectively. The CFD simulations suggest that the vortex core regions of the paired symmetrical reversing flow gradually move to the upwind region as the aspect ratio (H/W) of the nebkhas decreases. The size of the paired symmetrical reversing flows is reduced, and the merging of the reversing flows is prevented, potentially entraining the sediments far from the wake region. The sediments could rotate and deposit on both sides of the leeward face of the nebkhas and therefore contribute to the occurrence of short, tongue-like shadow dunes, which are particularly notable when H/W < 1. The vortex core region always occurs at the foot of the lee side of nebkhas with the same H/W regardless of the scale of the nebkhas or the incident wind speed.

Expression of Concern: Lattice Boltzmann Method Pore-scale simulation of fluid flow and heat transfer in porous media: effect of size and arrangement of obstacles into a channel

Expression of Concern: Lattice Boltzmann Method Pore-scale simulation of fluid flow and heat transfer in porous media: effect of size and arrangement of obstacles into a channel

Expression of Concern: The atomic obstacle size influence on the Hydrogen flow inside a nanochannel: A molecular dynamics approach to predict the fluid atomic arrangements

Expression of Concern: The atomic obstacle size influence on the Hydrogen flow inside a nanochannel: A molecular dynamics approach to predict the fluid atomic arrangements

Insights on structure-obstacle-soil interactions during the installation of monopiles for OWTs

ABSTRACT In this paper, a new three-dimensional FE model considering the structure-object-soil interaction is proposed to simulate the contact process during monopile installation. Using this model, the displacement vector diagrams and plastic strain contours of the obstacle and surrounding soil are obtained and analysed in detail to explain the soil failure mechanism and its effect on the installation resistance and moment profiles. Furthermore, the influences of the obstacle shape, size and contact position on the installation resistance of the monopile foundation are investigated. Results show that for obstacles with a dimensionless size (defined as the obstacle size to the monopile diameter) of 0.33, the resultant moment values exceed 1500kN·m, and the vertical resistance in the presence of obstacles is 0.88-1.53 times larger than that in the absence of obstacles. Further evaluation should be conducted to evaluate the effects of the resultant moments and vertical resistance on the actual installation process.

Lattice Boltzmann method based feedback control approach for pinned spiral waves

Spiral waves are common in nature and have received a lot of attention. Spiral wave is the source of ventricular tachycardia and fibrillation, and pinned spiral wave is less likely to be eliminated than free spiral wave. Therefore, it is important to find an effective method to control the pinned spiral wave. In this work, we investigate the feedback control approach to eliminating pinned spiral wave based on the lattice Boltzmann method, by using the FitzHugh-Nagumo model as an object. The numerical results show that the feedback control method has a good control effect on the pinned spiral wave no matter whether it is pinned on a circular or rectangular obstacle. In addition, the excitability coefficient, amplitude of feedback control, recording feedback signal time and obstacle size are systematically investigated by numerical simulation. The study shows that there are three cases of pinned spiral wave cancellation. Firstly, the amplitude of feedback control and excitability coefficient are related to the time required to eliminate the pinned spiral wave, and the larger the amplitude of feedback control signal or the smaller the excitability coefficient, the faster the cancellation of the pinned spiral waveis. Secondly, the size of the obstacle and the excitability coefficient affect the time interval between the time of recording the feedback signal and the time of adding the feedback control that can successfully control the pinned spiral wave. Finally, the recorded feedback signal time affects the minimum amplitude of feedback control required to successfully eliminate the pinned spiral wave, while the added feedback control time is constant. According to the discussion in this paper, it can be seen that the feedback control method has a good control effect on the pinned spiral wave.

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&lt;sup&gt;2&lt;/sup&gt; 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&lt;sub&gt;th&lt;/sub&gt;) and pumping power (P&lt;sub&gt;p&lt;/sub&gt;). 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.

An obstacle detection method for dual USVs based on SGNN-RMEN registration of dual-view point clouds

This paper proposes an unsupervised obstacle detection method for dual unmanned surface vessels (USVs) using the SGNN-RMEN framework. The method utilizes dual-view point clouds captured by two USVs to improve the detection of small obstacles under the condition of a visible shore. Firstly, a siamese graph neural network (SGNN) is designed to extract global contour features. A specialized task of global contour consistency classification is employed to ensure the interpretability of these features. Secondly, a rotation matrices estimation network (RMEN) is utilized to estimate the optimal rotation transformation for aligning point clouds based on the global contour features of the dual-view point clouds. The overlap degree between the dual-view point clouds before and after registration is used as feedback to train the model, enabling unsupervised learning. Finally, a " gridding - filtering - clustering” method is applied to annotate the size and position of obstacles based on the registration of the dual-view point clouds. Comparative experiments on two datasets demonstrate the effectiveness of the proposed method in accurately extracting contour features, achieving precise dual-view point cloud registration, and improving the detection rate of small obstacles in nearshore environments. The method also exhibits strong adaptability in unfamiliar marine environments.

Effects of exit obstacles on the evacuation dynamics of blind people

The modeling of blind people’s behavior is an important topic in pedestrian evacuation dynamics. In order to study movement characteristics of blind people in evacuation process and the effect of indoor obstacles on the evacuation efficiency of blind people, an extended cellular automata model is proposed to simulate blind people evacuation by considering the influence of obstacles. The control variable method is adopted to study the effect of indoor obstacles on the blind evacuation efficiency rule. The numerical simulation is applied to analyze the evacuation process of blind people under different setting (e.g. the location, size and other factors) of obstacles and different evacuation scenarios. The shunt effect of obstacles is discussed and the layout strategy of obstacles is optimized. The results show that the longitudinal obstacles in front of the exit can effectively play the diversion role of obstacles when the obstacle is at a certain distance from the exit, which will improve the evacuation efficiency of the blind. Furthermore, a horizontal obstacle of appropriate length can constrain the trajectory of the blind people and improve the efficiency of evacuation, but when the horizontal obstacle is too long, it will induce extra jam on both sides of the obstacle and hinder the evacuation of the blind. The finding can provide the theoretical basis for the blind people’s organization, management and the optimization of evacuation strategies during an emergency.