Layout Of Obstacles Research Articles

Pedestrian lane formation with following–overtaking model and measurement of system order

Pedestrian self-organizing movement plays a significant role in evacuation studies and architectural design. Lane formation, a typical self-organizing phenomenon, helps pedestrian system to become more orderly, the majority of following behavior model and overtaking behavior model are imprecise and unrealistic compared with pedestrian movement in the real world. In this study, a pedestrian dynamic model considering detailed modelling of the following behavior and overtaking behavior is constructed, and a method of measuring the lane formation and pedestrian system order based on information entropy is proposed. Simulation and analysis demonstrate that the following and avoidance behaviors are important factors of lane formation. A high tendency of following results in good lane formation. Both non-selective following behavior and aggressive overtaking behavior cause the system order to decrease. The most orderly following strategy for a pedestrian is to overtake the former pedestrian whose speed is lower than approximately 70% of his own. The influence of the obstacle layout on pedestrian lane and egress efficiency is also studied with this model. The presence of a small obstacle does not obstruct the walking of pedestrians; in contrast, it may help to improve the egress efficiency by guiding the pedestrian flow and mitigating the reduction of pedestrian system orderliness.

Modeling of non-homogeneous premixed hydrogen-air flame acceleration and deflagration to detonation transition in an obstructed channel

This paper uses Large Eddy Simulation (LES) technology to study the dynamic behavior of flame acceleration (FA) and deflagration-to-detonation transition (DDT) in a duct with different obstacle layouts in non-homogeneous concentration fields. A turbulent premixed combustion model with three additional source terms was established using the OpenFoam code library. It was found that the predicted results of the coupled model were in good agreement with the measured values of the experiment. Numerical results show that turbulent combustion and self-ignition effects are the main factors affecting flame acceleration. Still, self-ignition effects are a necessary and sufficient condition for inducing DDT phenomena. Detonation flames have around-flow and diffraction effects and do not evolve into jet and vortex flames, which differ from deflagration flames. Two initiation mechanisms were found under different obstacle layouts: hotspots were generated in the area swept by the Mach stem at the flame front, triggering detonation near the turbulent flame through the reactive gradient mechanism; focusing of sufficiently strong reflected waves deposited enough energy in a particular area near the flame brush and directly triggered detonation. In addition, the central obstacle layout is most conducive to FA and DDT, while the symmetrical layout is the least favorable.

Pedestrian Simulation on Evacuation Behavior in Teaching Building of Primary School Emergencies and Optimized Design

The spatial layout and arrangement of obstacles in the built environment significantly affect its evacuation performance. However, few researchers focus on pedestrian simulation-based design optimization of built environment under emergency evacuation conditions. In this paper, we aim to evaluate the evacuation performance of optimized design solutions for traffic space in the teaching building of a primary school based on a pedestrian simulation approach and to quantify the effect of design parameters on evacuation time. Firstly, the level of traffic space design parameters was determined and optimized design solutions for the traffic space of the school building were generated. Secondly, based on the Anylogic simulation platform, the environment module and pedestrian evacuation behaviour rules of the teaching building were built to realize the evacuation behaviour simulation. Thirdly, the effect of the traffic space design parameters on the evacuation time of the teaching building was evaluated and the most significant design parameters were identified. Finally, the optimal combination of traffic space design parameters was proposed under evacuation performance orientation. The results show that the sensitivity of the traffic space design parameters to evacuation time is 31.85%. The effect of corridor width on evacuation time is 49.06 times greater than the staircase width. The optimal design combination for the traffic space in the teaching building of the primary school is a 3.0 m wide trapezoidal corridor combined with a 3.6 m wide staircase, and a 3.0 m wide fish maw corridor combined with 3.6 m wide staircase, guided by evacuation performance. The framework developed in this paper provides technical support for the development of evacuation performance-oriented design optimization of the built environment, and the results are intended to supplement the building design specifications.

A modified Q-learning path planning approach using distortion concept and optimization in dynamic environment for autonomous mobile robot

Autonomous mobile robot path planning in unknown and dynamic environment is a crucial task for successful mobile robot navigation. This study proposes an improved Q-learning (IQL) algorithm to address the challenges of path planning in such environments. To this end, three different modes are introduced into the IQL algorithm, namely the normal mode, the distortion mode, and the optimization mode. The normal mode operates according to the standard Q-learning procedures. The distortion mode distorts the Q-values of states around dynamic obstacles to facilitate avoidance, while the optimization mode is employed to overcome the local minimum problem. The efficacy of the IQL algorithm is assessed through a series of comparative studies involving fourteen navigation environments, each with distinct obstacle layouts and types. Comparative analyses are performed based on several metrics, including computational time, travelled distance, collision rate, and success rate. The proposed IQL algorithm exhibits a lower collision rate and a higher success rate when compared to dynamic window approach, influence zone and inflated A*.

The effect of obstacle layouts on regulating luggage-laden pedestrian flow through bottlenecks

Previous studies found that regulating luggage-laden pedestrian flow helps to reduce the negative influence caused by luggage. Inspired by this, we experimentally study the effect of obstacle layout on regulating luggage-laden pedestrian flow. Five distances between the obstacle and exit are considered. The main findings are as follows: (i) The obstacle position affects the lane formation but does not affect the spatial distance between luggage-laden pedestrians and the boundary. It is revealed that the exact distance parameter can be implied regardless of the distance from the exit when modelling luggage-laden pedestrian movement. (ii) The average speed at the bottleneck increases with the distance between the exit and obstacle regardless of the pedestrian with and without luggage. The sooner the luggage-laden crowd is regulated, the higher the crowd speed can be at the bottleneck. (iii) The deviation angles all rise immediately before the exit, which means that the actual movement direction of pedestrians before the exit is not towards the midpoint of the exit. In addition, the inflection point of the deviation angle is approximately 0.5 m from the exit regardless of the obstacle position, which is the validation parameter of the luggage-laden crowd modelling. The results concluded that luggage-laden pedestrian flow could be regulated, and quantitative parameters were proposed to model luggage-laden pedestrian movement through the bottleneck.

Effects of porous materials with different thickness and obstacle layout on methane/hydrogen mixture explosion with low hydrogen ratio

The effects of porous materials with different thickness and obstacle layout on the explosion of 10%H2/90%CH4 at stoichiometric condition were studied. Three kinds of porous materials with different thickness were selected in the experiment, which are 1 cm, 2 cm and 3 cm respectively. Three kinds of obstacle layout were designed, which are symmetrical distribution, ipsilateral distribution and staggered distribution. Results show that porous materials with different thickness can promote or inhibit the explosion flame and overpressure when the obstacles are symmetrically distributed. The quenching failure of 1 cm thick porous material is similar to the action of mesh obstacles, which accelerates the flame to break through the bondage of porous material and continue to propagate, with a maximum speed of 87.74 m/s. When the thickness of porous material is 2 cm and 3 cm, the solid structure increases, the energy absorption increases, the flame impact porous materials quench, and the overpressure peak decreases. The greater the thickness of porous material, the better the attenuation effect, and the maximum overpressure attenuation can reach 59.71%. The change of obstacle layout has an important impact on the flame propagation structure. Compared with the ipsilateral distribution and staggered distribution, when the obstacles are symmetrically distributed, the vortex dynamic induced flame turbulence area is larger, the flame combustion rate is increased, and the explosion hazard is greater.

Revisiting the level-of-service framework for pedestrian comfortability: Velocity depicts more accurate perceived congestion than local density

The evaluation of pedestrian comfortability is important for the construction and management of walkable spaces. Pedestrian level-of-service (LOS), which is mostly categorized by density, has been widely applied and is believed to be capable of indicating the comfortability of the crowd. However, there is a lack of evidence that physically measured LOS reflects psychological comfortability, let alone the comparison between the performances of different candidate indicators, including the velocity and different local densities. Here, we show that walking velocity depicts pedestrian perceived congestion more accurately than density. In our experiments on pedestrians in a room-egress scenario with an inner obstacle, we obtained objective physical trajectory data from video analysis as well as subjective perception data from a questionnaire survey. The performance of the velocity and four types of local densities in reproducing pedestrian perceptions were numerically evaluated. We found that the velocity outperformed the local density. The lower performance of local densities was mainly caused by the pedestrians located at the back of the crowd, who walked at lower velocities and perceived higher congestion, despite their lower local densities that would correspond to less crowdedness from a physical viewpoint. Besides, the perceived congestion of pedestrians was shown to be affected by the initial pedestrian positions at the crowd, the obstacle layout, and the pedestrians’ age and gender. Furthermore, we suggest that the larger the gap between the desired and actual velocities, the larger the extent of the perceived congestion. We expect that our findings will contribute to a more accurate evaluation of pedestrian comfortability, which could help improve the walkable spaces of various infrastructures.

Effects of obstacle layout and blockage ratio on flame acceleration and DDT in hydrogen-air mixture in a channel with an array of obstacles

Numerical simulations were performed to study flame acceleration and deflagration-to-detonation transition (DDT) in hydrogen-air mixture in a channel with a two-dimensional array of cylindrical obstacles. A high-order numerical algorithm with adaptive mesh refinement was applied to solve reactive Navier-Stokes equations. The effect of obstacle layout was examined by considering three layouts at a fixed blockage ratio of 0.5: staggered, inline-concentrated, and inline-scattered. Three blockage ratios, 0.33, 0.5, and 0.67, were used for the case of staggered obstacles to explore the influence of blockage ratio. The results show that both obstacle layout and blockage ratio have significant effects on flame acceleration and DDT occurrence, although the basic mechanism of detonation initiation is consistent for all the cases involving shock focusing. In the staggered case, the head-on collisions of flame and pressure waves with obstacles greatly promote the growth of flame surface area and thus lead to the fastest flame acceleration and shortest detonation onset time. In the inline-concentrated case, flame propagates slower than that in the staggered case due to smaller flame surface area. However, compared to the zigzag path in the staggered case, the straight passages parallel to flame propagation direction in the inline-concentrated case are more conducive to producing strong shock focusing and thus result in the shortest DDT distance. In the inline-scattered case, the straight passage along the centerline of channel facilitates the early acceleration of flame, but it has the slowest flame propagation in lateral directions and thereby the longest DDT time and distance. For the staggered obstacles at different blockage ratios, flame acceleration rate increases with increasing blockage ratio. The occurrence of DDT is hindered by the most congested obstacles, because the shock focusing is insufficiently strong to initiate detonation after passing through the excessively narrow gaps.

Experimental study of path planning problem using EMCOA for a holonomic mobile robot

In this paper, a comparative study of the path planning problem using evolutionary algorithms, in comparison with classical methods such as the A∗ algorithm, is presented for a holonomic mobile robot. The configured navigation system, which consists of the integration of sensors sources, map formatting, global and local path planners, and the base controller, aims to enable the robot to follow the shortest smooth path delicately. Grid-based mapping is used for scoring paths efficiently, allowing the determination of collision-free trajectories from the initial to the target position. This work considers the evolutionary algorithms, the mutated cuckoo optimization algorithm (MCOA) and the genetic algorithm (GA), as a global planner to find the shortest safe path among others. A non-uniform motion coefficient is introduced for MCOA in order to increase the performance of this algorithm. A series of experiments are accomplished and analyzed to confirm the performance of the global planner implemented on a holonomic mobile robot. The results of the experiments show the capacity of the planner framework with respect to the path planning problem under various obstacle layouts.

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.

Federated learning based atmospheric source term estimation in urban environments

Establishing an accurate and efficient source term estimation (STE) system is of great significance for identifying unknown gas leakage sources in urban environments. Many successful STE methods have been proposed, while most of them assume there is only one point source. However, the complicated urban atmospheric dispersion and the massive sensor data in distributed edge devices pose new challenges. To address these issues, this paper proposes a method to convert measured concentrations into visual features, which retains the characteristics of diffusion and the layout of obstacles. Then, a federated STE (FL-STE) framework is proposed to extract knowledge from local models collaboratively without collecting all privacy data, in which a deep neural network is used to recognize the relationship between visual features and source terms. Furthermore, we construct an urban dispersion dataset with multiple obstacles and sources by FDS simulation. Various empirical studies prove the efficiency of the proposed method.

A hybrid vibration mitigation method based on the crowd flow control and tuned mass damper on a footbridge

This study proposes a hybrid mitigation method based on the crowd flow control and the eddy current tuned mass damper to control the excessive vibration caused by the random crowd excitation. The vibration mitigation method is applied on an experimental footbridge under random crowd loads and then the mitigation performance is analyzed experimentally and numerically. The numerical method of the social force model is used to simulate pedestrians detour behaviour in a blocking scenario. The time-varying coupling model of the crowd-structure-tuned mass damper is established, and the structure response is investigated. A virtual three dimensional obstacle based on the pedestrian stereo vision on the laboratory footbridge is designed to avoid the accident that pedestrians may encounter caused by the actual obstacles. It was found that the numerical response is in an appropriate agreement with the experimental data, implying that the social force model can simulate the detour behaviour accurately. Finally, the mitigation strategies are numerically implemented on an indoor footbridge, and the factors influencing the vibration mitigation rate are further analyzed using three different layouts. The layouts include Layout 1, for forcing pedestrian diversion separation, and Layout 2, for generating a bottle neck effect, and Layout 3, a nonlinear layout mode of obstacles, which is a combination of Layouts 1 and 2. The results show that the performance of the proposed hybrid mitigation method is more effective than the single mitigation method. In addition, the results show that the number and layout of obstacles determine the mitigation efficiency. It was also found that the vibration mitigation rate of the hybrid method with Layout 3 increases with the crowd density and tends to be stable when the crowd density exceeds 0.92 ped./m2. In addition, the mixed layout scheme may have more advantages in controlling crowd motion under high crowd density, while the linear layout schemes have certain competitiveness under low crowd density.

CFD analysis and RSM optimization of obstacle layout in Tesla micromixer

Abstract As a kind of fast and efficient mixing equipment, micromixer has been applied to chemical reaction detection. Its application can not only save experimental samples but also reduce the experimental time. In micromixers, Tesla structure is widely used due to its simple structure and special flow mechanism. In this paper, CFD and response surface method are used to analyze and verify the flow field of the configuration of adding diamond obstacles in the Tesla mixer. The results show that the order of layout parameter weight from large to small is obstacle size > vertical offset > horizontal offset. And the Desirability was 0.806, the optimal diamond obstacle size is 46.35 μm and the optimal lateral offset is 18.78 μm. In addition, a constant value OF 20 μm is predicted as the optimal vertical offset of the micromixer. Compared with the Tesla-type micromixer without obstacles, the diamond-shaped barrier Tesla-type micromixer designed in this paper has higher mixing rate and lower pressure drop under the same conditions, which can be applied to chemical reactors, and can also help to improve the accuracy of chemical reaction. It can be demonstrated that the presented optimal design method of obstacles layout in Tesla mixer is a simple and effective technology to improve the liquid mixing in microfluidic devices, and it has a broad application prospect in chemical engineering.

Single base station positioning based on multipath parameter clustering in NLOS environment

This paper proposes a scattering area model for processing multipath parameters achieve single base station positioning. First of all, we construct a scattering area model based on the spatial layout of obstacles near the base station and then collect the multipath signals needed for positioning and extract parameters. Second, we use the joint clustering algorithm improved by k-means clustering and mean shift clustering algorithm to process the parameters and extract useful information. Third, the processed information is combined with the spatial layout information of the scattering area model to construct equations, and then the solving problem of equations is converted into a least-squares optimization problem. Finally, the Levenberg-Marquardt (LM) algorithm is used to solve the optimal solution and estimate the mobile target position. The simulation results show that the positioning algorithm in this paper can be used by a single base station to locate the target in an outdoor non-line-of-sight (NLOS) environment, and the accuracy is improved compared with the traditional positioning algorithm.

Simulation of the influence of spatial obstacles on evacuation pedestrian flow in walking facilities

In order to research the influence mechanism of spatial obstacles on evacuation pedestrian flow, simulations of pedestrian evacuation are carried out by using the improved dynamic parameter model based on cellular automata. A retardation coefficient is introduced to describe the effect of obstacles slowing down pedestrian movement. A special technique is adopted to calculate the shortest estimated distance (SED) from cell site to exit considering obstacle layout and retardation coefficient. The repulsion and isolation effect of obstacles on pedestrian flow is manifested by the clusters of evacuation path chains. The movement probability is considered to narrow the gap between the normal speed and simulated evacuation speed caused by spatial discretization. The effectiveness of movement probability is verified by theoretical analysis and simulation results. It is found that in evacuation from a walkway, the influence of retardation coefficient on evacuation time will be gradually weakened and stabilized with walkway width rising. The influence of obstacle layout on the selection of evacuation path will be observed in the classroom. It also shows in the evacuation through an exit with a prepositive obstacle that the evacuation time is determined by the narrowest one in the series-connected bottlenecks. Moreover, the phenomena such as “pedestrians keeping a certain spatial distance from the boundaries of walkway”, “pedestrians preferring to choose a wider movement aisle in classroom” and “evacuation time being dominated by the narrowest one of series-connected bottlenecks” can also be observed during pedestrian evacuation in the simulation.

Experimental analysis and simulation study on turning behavior of pedestrians in L-shaped corridor

In our study, the unidirectional pedestrian flow in an L-shaped corridor is taken as the research object, and the pedestrian turning behavior is studied based on controllable experiments and micro simulations. First of all, three experimental scenarios, namely, no obstacles in the turning zone, diagonal layout of obstacles along the turning zone, and diagonal layout of obstacles in the vertical turning zone, are constructed. Behavioral characteristics such as pedestrian movement trajectory and velocity distribution are analyzed through controllable experiments of pedestrians. Then, a velocity correction model based on the Voronoi diagram is constructed, and the turning rules of pedestrians passing through a 90-degree L-shaped curve are embedded in the model. Finally, simulation research is conducted on the scene with both obstacles and asymmetric L-shaped corridors as well as the scene with neither of them to simulate and reproduce the turning behavior of pedestrians, and analyze the distributions of pedestrian velocities and individual densities at different stages. The research shows that when pedestrians move in a normal non-panic status, they rarely present disorderly behavior and always approach to the inside of the corner of the L-shaped corridor. In the turning area, pedestrians always follow their original moving mode to pass through the corner like a stable arc. And in the process of moving, pedestrians do not move in a straight line, but keep shaking back and forth for zipper effect. Besides, in the process of turning, the longer the distance from the center of the corner, the longer the distance of the pedestrian around the arc will be. And the L-shaped corridor can be divided into vertical straight area, transition area, turning area, and horizontal straight area. When pedestrians pass through the turning walking area, the “invisible bottleneck” phenomenon and the “curved triangle idle area” phenomenon can be observed. Besides, the streamline compression and multiple rows of pedestrian track clusters can be seen in the region. According to the characteristics of pedestrians walking through the L-shaped corridor, the turning rules of pedestrians are made, and the scene with both of obstacles and asymmetric L-shaped corridor as well as the scene with neither of them is simulated. Then, through the pedestrian simulation by using our model, the turning behavior of pedestrians passing through curve like a smooth arc can be effectively reproduced. Moreover, the “invisible bottleneck” phenomenon and the “curved triangle idle area” phenomenon in the turning walking area can be seen in the simulation. At the same time, when the pedestrian flow passes through the four areas of the L-shaped corridor successively, the velocity distribution is consistent with the experimental data of the pedestrian, showing an increasing-decreasing-increasing “wavy” change characteristic. The simulation model is also used to simulate the local density change of pedestrians due to the turning behavior, which verifies the unity of pedestrian velocity and local density change. The cognition of invisible bottleneck is helpful in rationally utilizing and designing the L-shaped corridor turning area.

Optimum path planning of elliptic and cubic nanoparticles using one and dual probe atomic force microscopes

In this article, optimum path planning of elliptic and cubic nanoparticles by one and dual probe atomic force microscopes is investigated. Four different parameters are considered in the cost function, including area under critical time–force diagram, critical indentation depth, path smoothness and area under force–time diagram of primary impact of nanoparticles. Also three different obstacles are added to process to make it more real. The layout of obstacles are various in each geometry. Since surfaces are rough, the effects of roughness (surface and particle) are considered in process. Genetic algorithm method has been used for path planning.

A multimesh finite element method for the Navier–Stokes equations based on projection methods

The multimesh finite element method is a technique for solving partial differential equations on multiple non-matching meshes by enforcing interface conditions using Nitsche’s method. Since the non-matching meshes can result in arbitrarily cut cells, additional stabilization terms are needed to obtain a stable method. In this contribution we extend the multimesh finite element method to the Navier–Stokes equations based on the incremental pressure-correction scheme. For each step in the pressure-correction scheme, we derive a multimesh finite element formulation with suitable stabilization terms. The proposed scheme is implemented for arbitrary many overlapping two dimensional domains, yielding expected spatial and temporal convergence rates for the Taylor–Green problem, and demonstrates good agreement for the drag and lift coefficients for the Turek–Schäfer benchmark (DFG benchmark 2D-3). Finally, we illustrate the capabilities of the proposed scheme by optimizing the layout of obstacles in a two dimensional channel.

Multi-Objective Genetic Algorithm-Based Autonomous Path Planning for Hinged-Tetro Reconfigurable Tiling Robot

Reconfigurable robots have received broad research interest due to the high dexterity they provide and the complex actions they could perform. Robots with reconfigurability are perfect candidates in tasks like exploration or rescue missions in environments with complicated obstacle layout or with dynamic obstacles. However, the automation of reconfigurable robots is more challenging than fix-shaped robots due to the increased possible combinations of robot actions and the navigation difficulty in obstacle-rich environments. This paper develops a systematic strategy to construct a model of hinged-Tetromino (hTetro) reconfigurable robot in the workspace and proposes a genetic algorithm-based method (hTetro-GA) to achieve path planning for hTetro robots. The proposed algorithm considers hTetro path planning as a multi-objective optimization problem and evaluates the performance of the outcome based on four customized fitness objective functions. In this work, the proposed hTetro-GA is tested in six virtual environments with various obstacle layouts and characteristics and with different population sizes. The algorithm generates Pareto-optimal solutions that achieve desire robot configurations in these settings, with O-shaped and I-shaped morphologies being the more efficient configurations selected from the genetic algorithm. The proposed algorithm is implemented and tested on real hTetro platform, and the framework of this work could be adopted to other robot platforms with multiple configurations to perform multi-objective based path planning.

Experimental verification of escape efficiency enhancement by the presence of obstacles

In emergency evacuation situations, placing an obstacle may be seen intuitively as a worse condition which may result in a slower evacuation time. Nevertheless, it is possible to lower the internal pressure in front of the exit and as a result preventing from clogging. This phenomenon has mainly been studied by numerical simulation, and so far the real-life human evacuation experiments considering different size, shape and placement of obstacles are rarely reported. In this paper, to verify the escape efficiency enhancement by the presence of obstacles and refine the experimental design, the simulation efforts are firstly carried out using the social force model. Then a series of real-life human evacuation experiments considering different types of obstacles are performed with the geometrical layouts suggested by social force model. It is observed the evacuation efficiency of pedestrians is actually quite sensitive to the geometrical parameters of obstacles, and the average evacuation time in human experiments can be reduced by suitable layout of obstacles. Compared to single-pillar obstacle, the panel and double-pillars obstacles are more robust and stable which could better improve the evacuation efficiency of pedestrians. Finally, to reveal the underlying mechanism of evacuation performance enhancement, the density profiles of pedestrians are compared based on the trajectories and Voronoi method. It is demonstrated that the essential physical mechanism behind the evacuation efficiency enhancement while placing an obstacle actually is a significant decrease of the density level in crowded region by effective separation in space.