Circular Obstacle Research Articles

Robust Collision Avoidance and Path‐Following of USVs With Reduced Conservativeness: A Control Barrier Function‐Based Approach

ABSTRACTThe collision avoidance and path‐following problem is fundamental for unmanned surface vehicles (USVs) to accomplish various tasks in different water environments. However, addressing this issue is challenging, as USVs are inevitably affected by environmental disturbances in practice. In this study, we address the robust collision avoidance path‐following problem for USVs with unknown bounded environmental disturbances by using the control barrier function (CBF)‐based approach. To reduce the conservativeness for the collision avoidance actions, the elliptical shape of the USV is considered when designing the control law. Furthermore, a high‐order control barrier function (HOCBF)‐based approach is proposed to achieve the robust collision avoidance with respect to both static and dynamic obstacles. Specifically, a nominal robust path‐following controller is first designed utilizing the predefined‐time observers without considering the collision avoidance requirement. Then, by considering the elliptical USV and the circular obstacles, collision avoidance input constraints are derived by the proper HOCBFs. Finally, a local quadratic programming (QP)‐based controller is proposed to achieve robust collision avoidance and path‐following of the USV. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed control strategy.

Heat Transfer and Entropy Generation on Free Convection Airflow inside a T-shaped Cavity Considering Inner Obstacles

In this study, a numerical analysis of heat and entropy generation on free convection of airflow is performed inside a T-shaped cavity with and without circular obstacles. The T-shaped cavity is formed with two symmetrically isothermal rectangular blocks. A cold temperature is maintained on the cavity's upper wall. The adiabatic walls are connected to heated wall at constant temperature. It is assumed that the flow is laminar, 2-D, and steadily incompressible. The finite element analysis is employed for solving the governing equations. The calculated results are compared and validated with the other published works. The dimensionless velocity (streamlines) and temperature (isotherms) are calculated and illustrated for varying Rayleigh numbers. It is found that the average Nusselt number at the heated walls and entropy generation inside the cavity increase with the increment of Rayleigh numbers. Moreover, the thermal performance effects on natural convection flow are investigated with circular obstacles inside the enclosure. Five cases without and with circular obstacles regarding the boundary conditions are investigated. It is found that the thermal performance of the cavity can be improved by adding two circular obstacles with cool boundary conditions. It is evident that the innovative structure by adding two circular obstacles with cool boundary conditions gives higher average Nusselt number and entropy generation whereas lower Bejan numbers for varying Rayleigh numbers. The study is performed for and . Jagannath University Journal of Science, Volume 11, Number 1, June 2024, pp. 186−202

Energy optimal path planning for wheeled mobile robots with circular obstacle

AbstractThe energy optimal motion planning algorithm for a differential drive robot with a circular obstacle in the maneuver space is introduced in this article. Rather than the traditional unicycle model, a non‐canonical state space model of the kinematics of a wheeled mobile robot is used to formulate the optimal control problem. The necessary conditions for optimality are formally derived using calculus of variations, resulting in constraints for the costates when the inequality constraint become active, revealing that the controls are required to be continuous. The optimality conditions permit decomposing the motion planning problem in two independent segments: prior to and after activation of the inequality constraints. Analytical expressions for the evolving states and control are found to be a function of Jacobi elliptic functions, permitting reducing the optimal control problem to a root‐finding problem. A comprehensive parametric study is included to demonstrate the impact on the optimal trajectories by varying the radius of the obstacle. The study shows that there are three distinct maneuver strategies with respect to the size of the obstacle. Furthermore, by including entering and exit time as optimization variables, a methodology for generalizing the development to any given motion scenario is developed and numerically illustrated.

Integrating angular and domain decomposition with space-angle discontinuous Galerkin methods in 2D radiative transfer

A space-angle discontinuous Galerkin (saDG) method is used to solve the steady-state radiative transfer equation (RTE) for 2D problems involving absorption, emission, and scattering for a semitransparent medium. This approach discretizes both spatial and angular domains. Parallel computing is based on angular decomposition (AD), and domain decomposition (DD) techniques. The DD technique directly solves the entire domain using the MUMPS library, whereas the AD technique results in an iterative approach for scattering media. This study proposes a novel hybrid AD-DD method, combining the best aspects of both techniques. Numerical results investigate the scalability, performance, and efficiency of AD and DD techniques. It is shown that a hybrid AD-DD technique is superior to these individual techniques by taking advantage of their strengths. Numerical methods demonstrate the applicability of the method of the best combination of hybrid AD-DD to 2D scattering gray media with complex geometries or enclosures with circular and square obstacles.

Substrate heterogeneities cause root growth trajectories to switch from vertical to oblique.

Hard pans, soil compaction, soil aggregation and stones create physical barriers that can affect the development of a root system. Roots are known to exploit paths of least resistance to avoid such obstacles, but the mechanism through which this is achieved is not well understood. Here, we combined 3D-printed substrates with a high-throughput live imaging platform to study the responses of plant roots to a range of physical barriers. Using image analysis algorithms, we determined the properties of growth trajectories and identified how the presence of rigid circular obstacles affects the ability of a primary root to maintain its vertical trajectory. Results showed the types of growth responses were limited, both vertical and oblique trajectories were found to be stable and influenced by the size of the obstacles. When obstacles were of intermediate sizes, trajectories were unstable and changed in nature through time. We formalised the conditions for root trajectory to change from vertical to oblique, linking the angle at which the root detaches from the obstacle to the root curvature due to gravitropism. Exploitation of paths of least resistance by a root may therefore be constrained by the ability of the root to curve and respond to gravitropic signals.

Redox flow battery:Flow field design based on bionic mechanism with different obstructions

All-vanadium redox flow batteries (VRFBs) are pivotal for achieving large-scale, long-term energy storage. A critical factor in the overall performance of VRFBs is the design of the flow field. Drawing inspiration from biomimetic leaf veins, this study proposes three flow fields incorporating differently shaped obstacles in the main flow channel. These designs aim to enhance the electrolyte diversion into branches, achieving a more uniform electrolyte distribution. Among these, the structure featuring circular obstacles demonstrated superior performance, exhibiting the lowest charging voltage and the highest discharging voltage. It also achieved the highest concentration uniformity of the active species (0.903). In comparison, at the flow rate of 3ml/s and the current density of 40mA cm−2, the efficiency based on pump power saw a maximum increase of 1.7 % and the efficiency based on output power experienced a maximum improvement of 2.5 %. This work offers a new direction in studying biomimetic flow field design and holds considerable potential for practical engineering applications.

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.

Numerical study on flame acceleration and deflagration-to-detonation transition affected by the solid obstacles with different shapes

To investigate which shape of solid obstacles is most optimal in terms of detonation-assisting capability within a closed channel, this study utilizes the Large Eddy Simulation (LES) method, based on the OpenFOAM platform, to conduct a detailed numerical study on the effects of different shaped obstacles (rectangular, rhombus, trapezoidal, circular, triangular) on flame acceleration and detonation initiation processes. The results show that the obstacles arranged in the middle of the combustion chamber can create more passages and local flames. Meanwhile, changes in the shape of obstacles can also produce different vortex structures and recirculation zones. These differences affect the flame surface area and the total combustion heat release rate, thereby affecting the flame acceleration effect. Judging from the results, triangular obstacles have the best flame acceleration effect, followed by rhombus, trapezoid, rectangle, and circular obstacles. In terms of detonation initiation, the obstacles with a slope can induce vortex to detach earlier, which produce a better vortex-flame interaction. Simultaneously, the slope can reflect the shock wave more frequently, creating more favourable conditions for the formation of Mach reflection and Mach stem. Based on this, it is found that trapezoidal and triangular obstacles have better detonation-assisting capability. Additionally, it is found that the stronger the leading shock wave and the shorter the distance between it and the flame front, the better the detonation initiation effect. In general, the types of detonation initiation in this study all belong to the shock detonation transition (SDT). However, the detonation initiation process can be further classified into two categories: (I) Detonation induced by shock wave reflection; (II) Detonation triggered by shock wave focusing.

Influence of solid cylinders on fluid flow and thermal analysis in a curved channel with constant magnetic field

The current study explores the numerical simulation of constant mixed convection heat transfer and fluid flow within a channel, driven by the inlet velocity. The investigation focuses on a curved irregular channel where the presence of three differently sized circular obstacles introduces an unpredictable element to the heat transfer process. For the two-dimensional physical scenario, mathematical equations are formulated to analyze velocity and temperature. Employing appropriate dimensional variables, the coupled partial differential equations are transformed into dimensionless form. Subsequently, the Finite Element Method (FEM) is employed to simulate the results for non-dimensional physical parameters such as Reynolds number, Richardson number, Hartmann number, nanoparticles' volume fraction, and various states of the circular obstacles on heated lines, flow structure, velocities, and temperatures at mean positions generating isotherms, streamlines, velocity, and temperature profiles for various parameter increments. The analysis reveals significant influences of Reynolds number (Re) and heated circular obstacles on the temperature profile, manifesting as heated lines within the system. The analysis brings to light the substantial impacts of nanoparticles on the temperature profile at both the vertical and horizontal mean positions. An elevated Hartmann number signifies a more robust magnetic field than viscous forces. A heightened magnetic field can hinder fluid movement and modify the patterns of heat transfer. Based on the graphical results, we infer that temperature differences tend to arise between strata as the Richardson number increases, leading to a heightened and more evident stratification.

Lid-driven effect on convective heat transfer with heated rods in a modified equilateral triangular cavity

This article presents heat transfer analysis at the walls of a circular heated obstacle under the influence of force and natural convection in a triangular domain. The circular obstacle is fixed at the center of triangular domain. The circular obstacle and the inclined walls differ in temperature (Th>Tc). The flow and heat transfer in the computational domain are caused by lid movement and temperature gradient. The triangular cavity is filled with air. The physical setup is described in terms of a system of differential equations. The dimensionless equations are solved using the Finite Volume Method (FVM). The results are computed for various flow controlling variables and presented in the form of isotherms, contours, tabular values and curves. The finding reveals that larger Reynolds number and Grashof number tend to higher heat transfer at the surfaces of heated obstacle. The average Nusselt number is noted to be maximum at w1 in the third quadrant when compared with the other walls of the heated obstacle. The results are compared with literature results in the limiting case.

Application of uniform experimental design theory to multi-strategy improved sparrow search algorithm for UAV path planning

The sparrow search algorithm (SSA) is a meta-heuristic optimization algorithm based on the predatory behavior of sparrows. However, SSA tends to fall into the local optimum when solving optimization problems with complex constraints. To improve its optimization efficiency and overall performance, this paper develops a multi-strategy improved SSA (ISSA) based on uniform experimental design theory. Specifically, the wrap-around L2-discrepancy (WD), as a uniformity metric for uniform design of experiments, is fully utilized with macro-regulation, adaptive dynamic management strategy, and boundary redistribution management mechanism to quantify the population uniformity in each iteration of ISSA. Inspired by the concept of uniform design, WD is initially adopted to gauge population uniformity, and the threshold acceptance (TA) algorithm is employed to produce an initial population with improved uniformity, hence augmenting the population’s diversity and quickening the rate of convergence. Secondly, a macroscopical individual iterative strategy of the producer is adjusted to avoid the population converging to the origin. Then, a dynamic population uniformity affiliation function based on WD is introduced to adjust the population uniformity affiliation function according to the relative amount of change in the global optimum, and the number of danger perceivers is adjusted according to the affiliation function. What is more, a new boundary update strategy is also proposed in ISSA based on population uniformity. By comparing ISSA on 23 standard test functions and recently updated validation function set CEC2022 with the original SSA, and some classical as well as newly developed algorithms, the superiority of the present ISSA is thoroughly confirmed. As an application case, the ISSA algorithm is utilized to solve the path planning problem of the complex environment of unmanned aerial vehicle (UAV) based on threat models by applying it to 2D maps containing circular and polygonal obstacles, as well as 3D maps containing mountain peaks and cylindrical obstacles. The simulation results show that ISSA can find more effective routes through various environments with obstacles.

Spontaneous path tracing in task-irrelevant mazes: Spatial affordances trigger dynamic visual routines.

Given a maze (e.g., in a book of puzzles), you might solve it by drawing out paths with your pencil. But even without a pencil, you might naturally find yourself mentally tracing along various paths. This "mental path tracing" may intuitively seem to depend on your (overt, conscious, voluntary) goal of wanting to get out of the maze, but might it also occur spontaneously-as a result of simply seeing the maze, via a kind of dynamic visual routine? Here, observers simply had to compare the visual properties of two probes presented in a maze. The maze itself was entirely task irrelevant, but we predicted that simply seeing the maze's visual structure would "afford" incidental mental path tracing (à la Gibson). Across four experiments, observers were slower to compare probes that were further from each other along the paths, even when controlling for lower level properties (such as the probes' brute linear separation, ignoring the maze "walls"). These results also generalized beyond mazes to other unfamiliar displays with task-irrelevant circular obstacles. This novel combination of two prominent themes from our field-affordances and visual routines-suggests that at least some visual routines may not require voluntary goals; instead, they may operate in an automatic (incidental, stimulus-driven) fashion, as a part of visual processing itself. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

General hydrodynamic features of elastoviscoplastic fluid flows through randomised porous media

A numerical study of yield-stress fluids flowing in porous media is presented. The porous media is randomly constructed by non-overlapping mono-dispersed circular obstacles. Two class of rheological models are investigated: elastoviscoplastic fluids (i.e. Saramito model) and viscoplastic fluids (i.e. Bingham model). A wide range of practical Weissenberg and Bingham numbers is studied at three different levels of porosities of the media. The emphasis is on revealing some physical transport mechanisms of yield-stress fluids in porous media when the elastic behaviour of this kind of fluids is incorporated. Thus, computations of elastoviscoplastic fluids are performed and are compared with the viscoplastic fluid flow properties. At a constant Weissenberg number, the pressure drop increases both with the Bingham number and the solid volume fraction of obstacles. However, the effect of elasticity is less trivial. At low Bingham numbers, the pressure drop of an elastoviscoplastic fluid increases compared to a viscoplastic fluid, while at high Bingham numbers we observe drag reduction by elasticity. At the yield limit (i.e. infinitely large Bingham numbers), elasticity of the fluid systematically promotes yielding: elastic stresses help the fluid to overcome the yield stress resistance at smaller pressure gradients. We observe that elastic effects increase with both Weissenberg and Bingham numbers. In both cases, elastic effects finally make the elastoviscoplastic flow unsteady, which consequently can result in chaos and turbulence.Graphical abstract

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.

Numerical analysis of unsteady free convection under the combined influence of inclined magnetohydrodynamic and exothermic chemical reaction in an enclosure filled with nanofluid

Unsteady study of the natural convection of aluminum oxide-water nanofluid within a trapezoidal geometry containing a circular cylinder located at its center. Finite Element method has been considered for the numerical analysis. The proposed investigation handled the impact of Rayleigh number (103–105), chemical reaction parameter (0–4), aluminum oxide nanoparticles volume fraction (0–0.06), magnetic field (0–63) and its inclination angle (0°–90°), and circular obstacle diameter (0.3–0.7) effects on time-dependent natural convection of Al2O3–H2O nanofluid. On the other hand, the value of Prandtl number has kept constant at (Pr = 6.2). Since the nanofluid mobility at φ = 0.02, Ha = 3, and Fk = 1 significantly improved, the heat transfer rate achieved its maximum intensity at Ra = 105. Research also reveals a little effect on heat transfer by increasing the fraction of nanoparticles. Additionally, as Ha intensifies from 0 to 63, a final change in the mean Nusselt number of 28.65 % is displayed. Finally, as the magnetic field angle of rotation is diminished, more enhancement in heat transmission is achieved. This research provides insights into the intricate relationship between natural convection and exothermic reaction under the influences of various conditions. This can illustrate the flow and thermal behaviors of nanofluid in such non-uniform shapes in many engineering applications.

Characterizing natural convection and thermal behavior in a square cavity with curvilinear corners and central circular obstacles

Thermal analysis through natural convection and heated obstacles in a different shape of cavity become an emerging concept among the scientific community. In this framework, this study investigates the natural convection phenomena occurring within a square cavity featuring a non-standard curvilinear shape and internally placed circular obstacles. The analysis focuses on the heat and fluid flow behavior in this unique geometrical configuration, exploring the influence of curvilinear boundaries and obstacles on convective heat transfer. The flow is assumed steady, laminar, and incompressible whereas a magnetic field with strength B0 is applied perpendicular to the fluid flow. No slip conditions are applied on each surface. The curvilinear corners and the inner circular obstacle are kept hot and the others including the bottom, left, right, and top walls are considered at cold temperatures. Numerical simulations are conducted to elucidate the complex interactions between the thermal gradients and fluid motion induced by the presence of circular obstacles. Galerkin finite element method is applied. The code validation and comparison with the existing data are being made. It is demonstrated that the local Nusselt number depends upon Rayleigh numbers, obstruction size, and Hartmann numbers. As the obstacles radius increases from 0.1 to 0.3, the temperature distribution in the middle of the cavity increases by almost 400%. This aids engineering in the manipulation of the heat transfer equipment used in this investigation. Around four corners, the local minimum Nusselt number rises by almost 97% as the radius increases from 0.1 to 0.3. These findings offer insightful knowledge about the fluid's dynamic behavior and a nice understanding of the roles played by geometric features, buoyancy-driven convection, and magnetic effects in the overall dynamics of heat transfer in industrial thermal processes. This knowledge aids scientists in designing suitable heat exchangers based on actual conditions.

Improved Collision Avoidance Algorithm of Autonomous Rice Transplanter Based on Virtual Goal Point

To ensure the operation safety and efficiency of an autonomous rice transplanter, a path planning method of obstacle avoidance based on the improved artificial potential field is proposed. Firstly, the obstacles are divided into circular or elliptic obstacles according to the difference between the length and width of an obstacle as well as the angle between the vehicle’s forward direction and the length direction of the obstacle. Secondly, improved repulsive fields for circular and elliptic models are developed. To escape the local minimum and goal inaccessibility of the traditional artificial potential field as well as meet the requirements of agronomy and vehicle kinematics constraints, the adaptive setting and adjusting strategy for virtual goal points is proposed according to relative azimuth between obstacle and vehicle. The path smoothing method based on the B-spline interpolation method is presented. Finally, the intelligent obstacle avoidance algorithm is designed, and the path evaluation rule is given to obtain the low-cost, non-collision, smooth and shortest obstacle avoidance path. To verify the effectiveness of the proposed obstacle avoidance algorithm, simulation and field experiments are conducted. Simulation and experimental results demonstrate that the proposed improved collision avoidance algorithm is highly effective and realizable.

Mixing performance of T-shaped wavy-walled micromixers with embedded obstacles

This research systematically investigates the impact of microchannel geometry on key parameters governing mixing efficiency and cost. The study focuses on passive T-shaped micromixers with modified sinusoidal wavy walls, analyzing a spectrum of configurations ranging from the raccoon to serpentine by varying the wall phase angles. The traditional T-shaped micromixer serves as a foundational reference, and we systematically vary phase angles, amplitudes, and wavelengths of the wavy walls to comprehensively address all possible configurations. Additionally, different shaped obstacles such as circular, square, diamond, and triangular obstacles are strategically introduced to further enhance mixing performance. The findings reveal intricate relationships and dependencies among geometric factors, shedding light on configurations that significantly enhance mixing efficiencies. Notably, a specific wavy micromixer configuration, characterized by a carefully tuned phase difference, amplitude, and wavelength, exhibits the highest mixing index in the absence of obstacles. The introduction of obstacles, particularly circular ones, further enhances mixing efficiency. As Reynolds (Re) and Schmidt (Sc) numbers increase, the mixing index decreases, and the mixing cost rises. This work adds a quantitative dimension to understanding the interplay between geometric parameters, flow conditions, and mixing performance in passive micromixers with systematic wavy walls and embedded obstacles.

Collective dynamics of active dumbbells near a circular obstacle.

In this article, we present the collective dynamics of active dumbbells in the presence of a static circular obstacle using Brownian dynamics simulation. The active dumbbells aggregate on the surface of a circular obstacle beyond a critical radius. The aggregation is non-uniform along the circumference, and the aggregate size increases with the activity (Pe) and the curvature radius (Ro). The dense aggregate of active dumbbells displays persistent rotational motion with a certain angular speed, which linearly increases with activity. Furthermore, we show a strong polar ordering of the active dumbbells within the aggregate. The polar ordering exhibits long-range correlation, with the correlation length corresponding to the aggregate size. Additionally, we show that the residence time of an active dumbbell on the obstacle surface increases rapidly with area fraction due to many-body interactions that lead to a slowdown of the rotational diffusion. This article further considers the dynamical behavior of a tracer particle in the solution of active dumbbells. Interestingly, the speed of the passive tracer particle displays a crossover from monotonically decreasing to increasing with the size of the tracer particle upon increasing the dumbbells' speed. Furthermore, the effective diffusion of the tracer particle displays non-monotonic behavior with the area fraction; the initial increase in diffusivity is followed by a decrease for a larger area fraction.

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.