Obstacle Size Research Articles

Practical Charger Placement Scheme for Wireless Rechargeable Sensor Networks with Obstacles

Benefitting from the maturation of Wireless Power Transfer technology, Wireless Rechargeable Sensor Networks have become a promising solution for prolonging network lifetime. In practical charging scenarios, obstacles are ubiquitous. However, most prior arts have failed to consider the combined impacts of the material, size, and location of obstacles on the charging performance, making these schemes unsuitable for real applications. In this article, we study a fundamental issue of W ireless ch A rger placement w I th obs T acles (WAIT), that is, how to place wireless chargers by comprehensively considering these parameters of obstacles, such that the overall charging utility is maximized. To tackle the WAIT problem, we first build a practical charging model with obstacles by introducing shadow fading, and conduct experiments to verify its correctness. Then, we design a piecewise constant function to approximate the nonlinear charging power. Afterwards, we develop a Dominating Coverage Set extraction algorithm to reduce the continuous solution space to a limited number. Finally, we prove the WAIT problem is a maximizing monotone submodular function problem, and propose a 1-1/e-ε approximation algorithm to address it. Extensive simulations and field experiments show that our scheme outperforms comparison algorithms by at least 20.6% in charging utility improvement.

Topological sensitivity analysis for the 3D nonlinear Navier–Stokes equations

This work is devoted to a topological asymptotic expansion for the nonlinear Navier–Stokes operator. We consider the 3D Navier–Stokes equations as a model problem and we derive a topological sensitivity analysis for a design function with respect to the insertion of a small obstacle inside the fluid flow domain. The asymptotic behavior of the perturbed velocity field with respect to the obstacle size is examined. The performed mathematical framework can be applied for a large class of design functions and arbitrarily shaped geometric perturbations. The obtained asymptotic formula can serve as a useful tool for solving a variety of topology optimization problems in fluid mechanics.

Self-healing properties of symmetrical power-exponent-phase vortices.

The self-healing properties of symmetrical power-exponent-phase vortices (SPEPVs) are analyzed in this paper. By placing an obstacle in the optical path of SPEPVs, we simulated the propagation of the obstructed SPEPVs and verified the self-healing of the beam theoretically. We also explored the influence of external factors (e.g.,obstacle size and position) and internal parameters (topological charge l and power exponent n) on the self-healing effect of obstructed SPEPVs. Furthermore, the energy flow density, similarity coefficient, effective self-healing distance, and diffraction efficiency of the obstructed SPEPVs were also discussed. The results demonstrated that the transverse energy flows around the obstructed region of SPEPVs will recover with the propagation distance increased, and the effective self-healing distance gradually increases linearly with the obstacle size r x increased. The self-healing characteristic gives the petal-like SPEPVs the ability to trap microparticles three-dimensionally.

Effect of magnetic nanofluid on cooling of hot obstacles in a minichannel: Optimization of obstacle size and spacing

This study conducts a numerical simulation of laminar flow of water/alumina nanofluids (NFs) in a channel with 5 hot obstacles. Obstacles and the wall beneath them have a high temperature, and the top wall is insulated. Also, the beginning and end parts of the bottom wall are insulated. The low-temperature homogenous NFs flow increases in temperature after hitting the obstacles and leaves the channel of length 20. Under the obstacles and the hot wall, a downward magnetic field of constant strength is applied. By altering the height of obstacles (HOB) between 0.1 and 0.7, the width between 0.1 and 1, and spacing between 0.1 and 1, the streamlines, temperature, local Nu, and average Nusselt number (Nu) are examined in the channel. In addition, the response surface methodology is used to conduct an optimization to obtain the maximum Nu and maximum outlet NFs temperature (T-NFs) in the channel by changing the mentioned parameters in associated ranges. The control volume method and Simple algorithm are used for simulations. Results of this study indicated that increasing the obstacle spacing and height causes the local Nu on the bottom wall to increase, the T-NFs in the middle of channel to increase, and the Nu in the channel to decrease. The maximum Nu occurs for the minimum obstacle size and smallest obstacle spacing; in this case, the Nu is higher by 611% than that of the case with maximum obstacle size and largest obstacle spacing.

An experimental and numerical analysis of natural convection in a partially open cuboid enclosure with a cylindrical obstacle

Natural convection in partially open enclosures has been area of intensive research in the past. However, a dearth of experimental or numerical studies has been found on the effect of cylindrical obstacle size on natural convection in such an enclosure. To address this gap, this study employs real-time experimental analysis using a non-invasive technique (Mach-Zehnder interferometry), that provides temperature distribution of flowing fluid in the investigating domain. The experiments are conducted in a partially open cuboid enclosure with an internal heat source on the bottom wall and a centrally placed cylindrical obstacle. The partial opening occupies 50% of the height of the left vertical wall. The study investigates the effect of obstacle diameter and Rayleigh number on natural convection through experimentation and numerical simulations using ANSYS Fluent 2020. An air velocity transducer is used to measure velocity at the opening. The interferograms obtained from the experiment are used to characterize the natural convection and compared with the results obtained from the numerical investigation. Fringes intensify at higher Rayleigh number, and the temperature gradient near the heat source increases with increase in obstacle diameter. The average Nusselt number and average exit velocity of flowing fluid increase with increase in obstacle diameter and Rayleigh number. For Rayleigh numbers in the range of 107 to 108, a threefold increase in the obstacle diameter results in an average increment in Nusselt number by 22% and an increment in the average exit velocity by 25%.

A Molecular Dynamics Study on the Dislocation-Precipitate Interaction in a Nickel Based Superalloy during the Tensile Deformation.

In the present paper, the dislocation-precipitate interaction in the Inconel 718 superalloy is studied by means of molecular dynamics simulation. The atomistic model composed of the ellipsoidal Ni3Nb precipitate (γ″ phase) and the Ni matrix is constructed, and tensile tests on the composite Ni3Nb@Ni system along different loading directions are simulated. The dislocation propagation behaviors in the precipitate interior and at the surface of the precipitate are characterized. The results indicate that the dislocation shearing and bypassing simultaneously occur during plastic deformation. The contact position of the dislocation on the surface of the precipitate could affect the penetration depth of the dislocation. The maximum obstacle size, allowing for the dislocation shearing on the slip planes, is found to be close to 20 nm. The investigation of anisotropic plastic deformation behavior shows that the composite system under the loading direction along the major axis of the precipitate experiences stronger shear strain localizations than that with the loading direction along the minor axis of the precipitate. The precipitate size effect is quantified, indicating that the larger the precipitate, the lower the elastic limit of the flow stress of the composite system. The dislocation accumulations in the precipitate are also examined with the dislocation densities given on specific slip systems. These findings provide atomistic insights into the mechanical behavior of nickel-based superalloys with nano-precipitates.

Experimental and numerical study of heavy gas dispersion in presence of obstacle motion

Most of the current research on heavy gas dispersion focuses on how fixed obstacles affect gas spreading. The turbulence caused by the movements of people or traffic will significantly affect heavy gas dispersion. Accordingly, this study presents an investigation of heavy gas dispersion under the influence of moving obstacles, which is based on the dynamic mesh approach using computational fluid dynamics (CFD). A turbulence model suitable for such a condition has been developed, and we have designed a small-scale experiment to verify the model's viability. Consequently, the verified model is further applied to a full-scale scenario for a chemical factory where a chlorine leak triggers an evacuation movement. On the basis of this scenario, we simplify the massive escape crowd to a regular geometric model, and the effects of the speed and size of movable obstacles on gas dispersion have been investigated by means of the RNG k-ε model and the layering updating approach in the dynamic mesh.

Barchan Dunes Cruising Dune‐Size Obstacles

AbstractWe investigate the behavior of subaqueous barchans reaching dune‐size obstacles by carrying out experiments where we varied the obstacle shape and size, the flow strength, and the grains' properties. We found that a subaqueous barchan can pass over or bypass a dune‐size obstacle, or even be blocked, with some intermediate situations. In the bypass cases, the original barchan can split in two or more bedforms, redistributing sand in space. Finally, we propose a classification map in which the barchan behavior depends basically on two dimensionless parameters. Our results represent a step toward understanding how barchans behave in the presence of large obstacles, such as retaining walls, tubes and bridge pillars.

Deep Learning Vision System for Quadruped Robot Gait Pattern Regulation.

Robots with bio-inspired locomotion systems, such as quadruped robots, have recently attracted significant scientific interest, especially those designed to tackle missions in unstructured terrains, such as search-and-rescue robotics. On the other hand, artificial intelligence systems have allowed for the improvement and adaptation of the locomotion capabilities of these robots based on specific terrains, imitating the natural behavior of quadruped animals. The main contribution of this work is a method to adjust adaptive gait patterns to overcome unstructured terrains using the ARTU-R (A1 Rescue Task UPM Robot) quadruped robot based on a central pattern generator (CPG), and the automatic identification of terrain and characterization of its obstacles (number, size, position and superability analysis) through convolutional neural networks for pattern regulation. To develop this method, a study of dog gait patterns was carried out, with validation and adjustment through simulation on the robot model in ROS-Gazebo and subsequent transfer to the real robot. Outdoor tests were carried out to evaluate and validate the efficiency of the proposed method in terms of its percentage of success in overcoming stretches of unstructured terrains, as well as the kinematic and dynamic variables of the robot. The main results show that the proposed method has an efficiency of over 93% for terrain characterization (identification of terrain, segmentation and obstacle characterization) and over 91% success in overcoming unstructured terrains. This work was also compared against main developments in state-of-the-art and benchmark models.

Mathematical Modeling of pedestrian flow through the obstacle bottleneck

For pedestrians in walking facilities, their movements are often obstructed by bottlenecks where the walkable widths are geometrically reduced. In previous research, to reproduce the influence of bottlenecks on pedestrian movements, agent-based simulation models have been widely applied. However, their high reliability on modeling rules and parameters requires calibration at the microscopic level, which makes them difficult to apply from an engineering perspective. Here, we applied a mathematical approach, which estimates the egress efficiency based on the density-flow rate fundamental diagram, to reproduce the egress time of pedestrians in our field experiments. Both the obstacle and the exit were considered bottlenecks in our experiments. It was indicated that with the same width, the obstacle bottleneck acted as an ‘ineffective’ bottleneck that did not affect the egress time when it was near the exit bottleneck, whereas acted as an ‘effective’ bottleneck when it was distant from the exit bottleneck. To reproduce this phenomenon, we applied a mathematical approach that abstracts the walking scenario as a scheme with the bottlenecks as links and different regions as nodes. As a result, the egress times under different layouts were reproduced successfully by introducing the density-flow rate fundamental diagram into the scheme. Furthermore, a reasonable range of the obstacle size and obstacle-exit width, under which condition the egress time is constant, was estimated. This study can be applied to estimate the egress time of the walking facilities by considering the fundamentals of pedestrian flows from a mathematical perspective, thus helping in the actual design of bottlenecks that could ensure efficient and safe pedestrian egress in walking facilities.

Permeability in barrier membranes: Comparison between experiments, direct calculations, and analytical models

AbstractThis paper compares direct calculations, experimental data and analytical models in materials with controlled barrier microstructure. Confocal Raman was used to follow mass transport of a penetrant, hexadecanol (HDOL), through the barrier structure. produced by carving holes in specific positions and orientations in a polydimethylsiloxane (PDMS) matrix. Finite element method (FEM) was used to predict maps of HDOL concentration around the obstacles, which were directly compared to Raman data. Effective diffusion coefficients were obtained in homogeneized microstructures of slender obstacles in diluted and semi‐concentrated obstacles regimes. Results were compared with predictions of simple analytical models: Nielsen, Lape, those derived from the ideas of Bharadwaj (Greco; Greco and Maffezzolli), and those developed from FEM simulations (Minelli et al. and Dondero et al.). For the first time, predictions of these widely used analytical models could be tested against well‐controlled barrier membranes. The influence of obstacle orientation, size polydispersity and eventual aggregation, all features occurring in real polymeric nanocomposites are analyzed. Some limitations about the use of simple analytical models to interpret permeability data in real nanocomposites are discussed.

Based on the temperature correlation principle, the use of a magnetic obstacle to generate pulsations in the flow measurement of a liquid metal coolant

A promising method for determining the flow rate of a liquid metal coolant is the temperature correlation method (TCM) since it does not require calibration. However, being indirect, it has a number of limitations to be carefully studied. A magnetic obstacle is used as a temperature pulsation generator. The paper presents the results of a numerical study on the influence of the size of a magnetic obstacle and its activity ratio, as well as effect of the temperature difference between the liquid metal and the environment, on the performance and accuracy of the TCM. The main criteria influencing the operation of the method are identified, namely the extent and spatial position of the vorticity and mixing zones.

An Efficient Trajectory-Planning Method With a Reconfigurable Model for Any Tractor-Trailer Vehicle

Trajectory planning for a tractor-trailer vehicle (TTV) is a tough task even in a static environment because of its complicated kinematic constraints. This paper aims to efficiently plan an optimal trajectory with a reconfigurable model for any TTV in the static environment. A reconfigurable modelling method is first proposed to simulate the TTV with arbitrary number of trailers and hitching mode. Then, the planning task is formulated as a nonlinear optimal control problem. However, it is too difficult to be solved, and is time-consuming to find a feasible solution, let alone the optimal one. To this end, a novel guided solving method (GSM) is proposed to solve this problem progressively with great efficiency. GSM is divided into two steps. Step 1 plans rough trajectories for the TTV, taken as an initial guess for the next step. In step 2, the problem is split into a sequence of subproblems, solved by asynchronously expanding the size of both vehicle body and obstacles, speeding up the optimization process. Simulations are carried out in several complex cases, and four competitive algorithms are selected for comparison. The results show that the proposed method outperforms others in the feasibility and efficiency of problem-solving for trajectory planning. Specifically, the proposed method is feasible in all testing cases, and saves up to 81.4%, 83.2% and 55.9% solving time compared with other three methods in the 135° turn scenario, respectively, bringing the great improvement of planning efficiency.

Dynamic obstacle detection method based on U–V disparity and residual optical flow for autonomous driving

As a core step of obstacle avoidance and path planning, dynamic obstacle detection is critical for autonomous driving. This study aimed to propose a dynamic obstacle detection method based on U–V disparity and residual optical flow for autonomous driving. First, a drivable area of an unmanned vehicle was detected using U–V disparity images. Then, obstacles in the drivable area were detected using U–V disparity images and the geometric relationship between obstacle size and its disparity. Finally, the motion likelihood of each obstacle was estimated by compensating the camera ego-motion. The innovation of the proposed method was that the searching range of the moving obstacles was greatly narrowed by detecting the obstacles in the drivable area, which greatly improved not only the moving obstacle detection efficiency but also the detection accuracy. Datasets from the KITTI benchmark and our self-acquired campus scene data were chosen as testing samples. The experimental results showed that our method could achieve high detection precision, low missed detection rate and less time consumption.

Topological asymptotic expansion for the full Navier–Stokes equations

This paper is concerned with a topological sensitivity analysis for the two dimensional incompressible Navier–Stokes equations. We derive a topological asymptotic expansion for a shape functional with respect to the creation of a small geometric perturbation inside the fluid flow domain. The geometric perturbation is modeled as a small obstacle. The asymptotic behavior of the perturbed velocity field with respect to the obstacle size is discussed. The obtained results are valid for a large class of shape fonctions and arbitrarily shaped geometric perturbations. The established topological asymptotic expansion provides a useful tool for shape and topology optimization in fluid mechanics.

Give Me a Hand: Improving the Effectiveness of Near-field Augmented Reality Interactions By Avatarizing Users' End Effectors.

Inspired by previous works showing promise for AR self-avatarization - providing users with an augmented self avatar, we investigated whether avatarizing users' end-effectors (hands) improved their interaction performance on a near-field, obstacle avoidance, object retrieval task wherein users were tasked with retrieving a target object from a field of non-target obstacles for a number of trials. We employed a 3 (Augmented hand representation) X 2 (density of obstacles) X 2 (size of obstacles) X 2 (virtual light intensity) multi-factorial design, manipulating the presence/absence and anthropomorphic fidelity of augmented self-avatars overlaid on the user's real hands, as a between subjects factor across three experimental conditions: (1) No-Augmented Avatar (using only real hands); (2) Iconic-Augmented Avatar; (3) Realistic Augmented Avatar. Results indicated that self-avatarization improved interaction performance and was perceived as more usable regardless of the anthropomorphic fidelity of avatar. We also found that the virtual light intensity used in illuminating holograms affects how visible one's real hands are. Overall, our findings seem to indicate that interaction performance may improve when users are provided with a visual representation of the AR system's interacting layer in the form of an augmented self-avatar.

A study on flow field characteristics of a self-propelled robot fish approaching static obstacles based on artificial lateral line

To perceive the static obstacles in still water, the flow field characteristics of a self-propelled robot fish approaching static obstacles were studied based on artificial lateral line (ALL). The pressure distribution on the fish body surface was calculated with different separation between the robot fish and the obstacle boundary, obstacle size and undulating frequency. Subsequently, an ALL system was established and five obstacle perception models were studied to analyze the perceptual characteristics of the ALL. Finally, the experiments were conducted to further reveal the effects of obstacles and motion parameters on the body surface pressure of robot fish. The results indicate that the obstacles have a significant effect on the pressure distribution of the surface of the fish body. Namely the parameters of separation, obstacle size and undulating frequency will affect the peak value of the amplitude envelope of the pressure signals. The obstacle size and distance between the obstacles can be predicted using the time parameters of the amplitude envelope of the pressure signals. Moreover, the self-propelled robot fish with a medium undulating frequency approach to the large obstacles with small separation has better perceptual performance. The findings could offer some insight into understanding the perception of complex underwater environment based on ALL.

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

The flow characteristics at a pore-scale porous medium has a significant role to the development of cooling modules. Despite this fact, still there is no adequate knowledge about the effect of size, pattern and position of the obstacles, on fluid flow and heat transfer. In this work, fluid flow through the porous media and heat transfer have been modeled by means of the Single Relaxation Time SRT-LBM with BGK approximation and D2Q9 model. The effect of size and arrangement of cold square obstacles in a heated wall channel is investigated for incompressible flow in case of fixed porosity degree, ε=75%. Results are presented in terms of velocity and temperature fields, streamlines, and Nusselt number. The results show that, for the same porosity degree, by changing the number of the obstacles or their arrangement, the tortuosity changes and therefore velocity and temperature fields are modified, as well as local and average Nusselt number. The results show that, for the same porosity degree, by changing the number of the obstacles or their arrangements, the value of Nuavg of the channel walls and tortuosity increased up to 24.7% and 9%, respectively, in comparison with the Poiseuille flow.

Simulation Study on Suppressing Shielded Fires by Water Mist Systems

This article presents a numerical analysis of the performance of three water mist fire suppression systems, with different characteristics, on shielded fires as representing more realistic fire scenarios in an enclosure. A diesel pool fire with a peak heat release rate (HRR) value of 75 kW is covered by an obstacle above it with different shielding conditions to investigate the influence of the obstacle size and the vertical distance between the obstacle and the nozzle on the efficiency of the water mist systems. The obstacle prevents a large number of droplets from directly reaching the fuel surface and flames. The modeling and numerical analysis of this study were carried out by the fire dynamics simulator (FDS) programming tool, and the designed model was validated against the experimental data for both dry and wet tests. The results show that two of the analyzed mist sprays could successfully extinguish the shielded fires in a short time with an obstacle size of 25 cm × 25 cm and 50 cm × 50 cm, placed at two heights. However, the third mist system had a longer extinguishing time compared to the first two nozzles. All three nozzles failed to suppress the fire covered by the largest obstacle (1 m × 1 m). The shielding conditions and nozzle characteristics can affect the performance of water mist systems to some extent.

A simple catch: Fluctuations enable hydrodynamic trapping of microrollers by obstacles.

It is known that obstacles can hydrodynamically trap bacteria and synthetic microswimmers in orbits, where the trapping time heavily depends on the swimmer flow field and noise is needed to escape the trap. Here, we use experiments and simulations to investigate the trapping of microrollers by obstacles. Microrollers are rotating particles close to a bottom surface, which have a prescribed propulsion direction imposed by an external rotating magnetic field. The flow field that drives their motion is quite different from previously studied swimmers. We found that the trapping time can be controlled by modifying the obstacle size or the colloid-obstacle repulsive potential. We detail the mechanisms of the trapping and find two remarkable features: The microroller is confined in the wake of the obstacle, and it can only enter the trap with Brownian motion. While noise is usually needed to escape traps in dynamical systems, here, we show that it is the only means to reach the hydrodynamic attractor.