Trapezoidal Obstacle Research Articles

Shape of an obstacle affects the mediolateral trajectory of the lower limb during the crossing process.

In previous studies involving obstacle crossing, vertical foot clearance has been used as an indicator of the risk of contact. Under normal circumstances, individuals do not always cross over obstacles with the same height on both sides, and depending on the shape of the obstacle, the risk of contact may differ depending on the foot elevation position. Therefore, we investigated whether task-related control of the mediolateral foot position is adapted to the shape of the obstacle. Sixteen healthy young adults performed a task in which they crossed over two obstacles with different shapes while walking: a trapezoidal obstacle and a rectangular obstacle, as viewed from the frontal plane. It was shown that when crossing over a trapezoidal obstacle, the participants maintained foot clearance by controlling the mediolateral direction, which chose the height that needed to be cleared. The results of this study suggest that the lower limb movements that occur during obstacle crossing are controlled not only in the vertical direction but also in the mediolateral direction by adjusting the foot trajectory to reduce the risk of contact. It was demonstrated that control was not only based on the height of the obstacle directly under the foot but also in the foot mediolateral direction, considering the shape of the entire obstacle, including the opposite limb.

Numerical investigation of ternary particle separation in a microchannel with a wall-mounted obstacle using dielectrophoresis

In recent years, microfluidic-based particle/cell manipulation techniques have catalyzed significant advances in several fields of science. As an efficient, precise, and label-free particle/cell manipulation technique, dielectrophoresis (DEP) has recently attracted widespread attention. This paper presents the design and investigation of a straight sheathless 3D microchannel with a wall-mounted trapezoidal obstacle for continuous-flow separation of three different populations of polystyrene (PS) particles (5, 10 and 20 µm) using DEP. An OpenFOAM code is developed to simulate and investigate the movement of particles in the microchannel. Then, the code is validated by performing various experimental tests using a microdevice previously fabricated in our lab. By comparing the numerical simulation results with the experimental tests, it can be claimed that the newly developed solver is highly accurate, and its results agree well with experimental tests. Next, the effect of various operational and geometrical parameters such as obstacle height, applied voltage, electrode pairs angle, and flow rate on the efficient focusing and separation of particles are numerically investigated. The results showed that efficient particle separation could only be achieved for obstacle heights of more than 350 µm. Furthermore, the appropriate voltage range for efficient particle separation is increased by decreasing the electrode angle as well as increasing the flow rate. Moreover, the results showed that by employing the appropriate channel design and operational conditions, at a maximum applied voltage of 10V, a sample flow rate of 2.5μL/min could be processed. The proposed design can be beneficial for integrating with lab-on-a-chip and clinical diagnosis applications due to advantages, such as simple design, no need for sheath flow, the simultaneous ternary separation of particles, and providing precise particle separation.

Numerical Study and Geometrical Investigation of an Onshore Overtopping Device Wave Energy Converter with a Seabed Coupled Structure

Studies regarding renewable energy sources have gained attention over recent years. One example is wave energy converters, which harvest energy from sea waves using different operational principles such as oscillating water columns, oscillating bodies, and overtopping devices. In the present paper, a numerical study is carried out, and a geometrical investigation of a full-scale overtopping device with a coupled structure mounted on the seabed is performed using the Constructal Design method. The main purpose is to investigate the influence of the design over the available power of the device. The areas of the overtopping ramp (Ar) and the trapezoidal seabed structure (At) are the problem constraints. Two degrees of freedom are studied, the ratio between the height and length of the ramp (H3/L3) and the ratio between the upper and lower basis of the trapezoidal obstacle (L1/L2). The device submersion is kept constant (H1 = 3.5 m). The equations of continuity, momentum, and the transport of volume fraction are solved with the Finite Volume Method, while the water–air mixture is treated with the multiphase model Volume of Fluid. Results showed that the ratio H3/L3 presented a higher sensibility than the ratio L1/L2 over the accumulated water in the reservoir. Despite that, the association of a structure coupled to the ramp of an overtopping device improved the performance of the converter by 30% compared to a conventional condition without the structure.

Hybrid Particle Swarm Optimization-based Modeling of Wireless Sensor Network Coverage Optimization

To address the problem of insufficient coverage of WSN and poor network coverage in obstacle environments, the study proposes an improved particle swarm optimization (PSO) combined with a hybrid grey wolf algorithm. The speed and position of the PSO particle's search for superiority are enhanced through the guiding nature of the superior wolf in the grey wolf optimization (GWO), thus the convergence speed and search precision are improved. Based on this, the study applies the improved PSO to a wireless sensor networks (WSO) coverage optimization model and uses model comparison to test the effectiveness and superiority of the algorithm. According to the results, the node network coverage of PSO, genetic algorithm (GA), data envelopment analysis (DEA), GWO, and grey wolf particle swarm optimization (GWPSO) reach 85.97%, 87.24%, 88.76%, 89.31%, and 91.05% respectively in the trapezoidal obstacle environment. And the node network coverage of the research-designed GWPSO algorithm reaches the highest value of its kind. This shows that the research-designed GWPSO has superior performance in the optimization control of sensor coverage deployment compared with similar algorithms. The design provides a new path for optimizing wireless sensor node network coverage.

拖拉机动量飞轮主动防侧翻控制与模型试验研究

The tractor working environment is complex and changeable, and the dynamic variation range of the center of gravity position of the tractor body is large. In order to avoid rollover accident, an active anti rollover control method of tractor momentum flywheel and its model test are proposed in this paper. The tractor dynamic system model and control strategy are verified by a 1:16 scale tractor model. The research results show that when the model tractor crosses the trapezoidal obstacle B, the roll angle of the whole machine is temporarily stable near 35 °, indicating that at this time, the tires on one side of the whole machine are in actual contact with the obstacle, showing a short stable state of the whole machine. When the pavement roughness reaches F-H level, without any active anti rollover control, the evaluation index EP shows a divergence trend when it is greater than 1, and the simulation calculation is terminated due to the occurrence of rollover of the whole machine. The test data and simulation results under two different driving speeds are in good agreement, which verifies the effectiveness and reliability of the tractor rollover dynamic system model and the momentum flywheel active stabilization system.

Node coverage optimization algorithm for wireless sensor networks based on improved grey wolf optimizer

Aiming at the problem of wireless sensor network node coverage optimization with obstacles in the monitoring area, based on the grey wolf optimizer algorithm, this paper proposes an improved grey wolf optimizer (IGWO) algorithm to improve the shortcomings of slow convergence, low search precision, and easy to fall into local optimum. Firstly, the nonlinear convergence factor is designed to balance the relationship between global search and local search. The elite strategy is introduced to protect the excellent individuals from being destroyed as the iteration proceeds. The original weighting strategy is improved, so that the leading wolf can guide the remaining grey wolves to prey in a more reasonable way. The design of the grey wolf’s boundary position strategy and the introduction of dynamic variation strategy enrich the population diversity and enhance the ability of the algorithm to jump out of local optimum. Then, the benchmark function is used to test the convergence performance of genetic algorithm, particle swarm optimization, grey wolf optimizer, and IGWO algorithm, which proves that the convergence performance of IGWO algorithm is better than the other three algorithms. Finally, the IGWO algorithm is applied to the deployment of wireless sensor networks with obstacles (rectangular obstacle, trapezoidal obstacle and triangular obstacles). Simulation results show that compared with GWO algorithm, IGWO algorithm can effectively improve the coverage of wireless sensor network nodes and obtain higher coverage rate with fewer nodes, thereby reducing the cost of deploying the network.

A geometrical path planning method for unmanned aerial vehicle in 2D/3D complex environment

This paper presents a geometrical path planning method, and it can help unmanned aerial vehicle to find a collision-free path in two-dimensional and three-dimensional (2D and 3D) complex environment quickly. First, a list of tree is designed to describe obstacles, and it is used to query the obstacles which block the line from starting point to finishing point (blocking obstacle). Specially, the list also stores the edge information of blocking obstacle. For the obstacles with short distance, a reasonable way to fly over is studied. Then, a shortest path planning method based on geometrical computation is proposed according to different shapes of obstacles. The obstacles are convex and divided into two cases of 2D and 3D. 2D environment includes rectangular obstacle, trapezoidal obstacle, triangular obstacle, circular obstacle and elliptic obstacle. In 3D, it includes cuboid, sphere and ellipsoid. To compare with other methods, the simulation is made in different environments. In 2D environment with circular obstacles, the method is similar to the artificial potential field. In 2D environment with rectangular obstacles, the performance of the proposed method is better than A-star. Compared with genetic algorithm, the proposed method gives a better result in 3D environment with cuboid obstacles. In 3D environment with hybrid obstacles, it is similar to interfered fluid dynamical system. Through comprehensive comparison and analysis, the conclusion is that the method has good adaptability and does not require grid modeling. It can find a shorter path in 2D/3D complex environment within a short time, so it has the ability of real-time path planning.

Experimental investigation of the propagation of deflagration flames in a horizontal underground channel containing obstacles

The deflagration of premixed methane–air gas (concentration of 9.5%) was experimentally investigated in a closed channel (0.2 m × 0.2 m × 6.5 m) containing different obstacles. Rectangular, trapezoidal, and spherical obstacles were employed. Various tests on the deflagration flames were carried out (using schlieren imaging and pressure and flame sensors) and the diverse characteristics of the deflagration flames were analyzed. In this work, we concentrate on the change in shape of the flames as they pass the obstacles, the instantaneous overpressure formed in the local areas in front and behind the obstacles, and the change in velocity of the deflagration flame. The results suggest that extremely complex changes occur when the deflagration flames pass the differently-shaped obstacles in the closed channel. The shape of the obstacle and the structural form of the confined space between the boundaries of the obstacle and channel walls both exert a significant effect on the mechanical characteristics of the deflagration flames as they develop. Obstacles in the channel enhance the propagation of the deflagration flame to unburned areas away from the local area where the flame forefront had been. The flatness of the flame front is therefore broken. A certain amount of flame stagnation appears to occur which results in a larger crosswise span of the flame front. The obstacle’s angles and effective barrier area presented to the incoming flow of the deflagration flame have an effect on the propagation of the flame and instantaneous overpressure of the deflagration flame in the local areas just in front and behind the obstacle. Moreover, the correlation between the obstacle angle and mainstream direction of the deflagration flame as it passes the obstacle also has an effect. Of the three obstacles investigated, the trapezoidal obstacle exhibits the weakest ability to strengthen the inertial force of the deflagration flame. Compared to the others, the spherical obstacle most significantly enhances the inertial force of the deflagration flame as it passes through the obstacle’s neighborhood.

Effect of porosity on an internal solitary wave propagating over a porous trapezoidal obstacle

A permeable seabed may influence the evolution of an internal solitary wave propagating on a continental shelf and nearshore. In order to study the porous effect, numerical simulations are performed to investigate the flow field and waveform inversion of a large depression ISW propagating over a porous trapezoidal obstacle. A finite volume based Cartesian grid method is adopted to solve the Reynolds averaged Navier-Stokes equations using a k-ε model for the turbulent closure and porous media model together. Numerical results reveal that waveform inversion weakens significantly, as the porosity of the obstacle increases, except when porosity nf<0.2. At the same time, the magnitude of vorticity and turbulent energy decrease remarkably due to acute reduction of the production term induced by percolation and wave-pore interaction. Moreover, a skewed hump shaped relation appears between the maximum vorticity and the porosity. For transmitted wave energy on a horizontal plateau, total energy may decrease as nf<0.2 but increases moderately while nf>0.2 during a strong wave-obstacle interaction.

The induced shock and impact force as affected by the obstacle geometric factors during tire-obstacle collision dynamics

The knowledge on vehicle stability, ride comfort and performance is critically significant on off-road vehicle traversing over irregular terrains. The subject of off-road vehicle analysis from the terrain–tire interaction perspective has always been from complex domains of engineering owing to the elasto-plastic behavior of deformable terrain and nonlinear vehicle dynamics. This paper is dedicated to synthesize the induced shock and impact force as affected by the obstacle geometric factors during tire-obstacle collision dynamics. To this end, various obstacle shapes were included at different depths to determine at which geometric configuration, the greatest and lowest impact forces are induced. Aiming this, the soil bin facility equipped with a single-wheel tester of Urmia University was adopted to carry out the needed experimental tests while the operational condition of the wheel traversing was absolutely controllable (i.e. slip, forward speed, wheel load, etc.). The developed model also was verified by the experimental data and the obtained results showed that the greatest impact force both at the longitudinally and vertically oriented directions were obtained by the triangular shaped obstacle at the greatest height while in contradictory to the expectations, the lowest values were obtained for the trapezoidal obstacle when compared with the Gaussian shaped obstacle. The findings will serve future studies as a functional source to develop improved vehicle designs to interact with differently shaped obstacles and various operational conditions for run-off-road vehicles traversing over irregularities.

Effects of varying pycnocline thickness on interfacial wave generation and propagation

Interfacial solitary waves (ISWs) can be observed in stratified ocean and laboratory flumes which generally comprise a pycnocline in finite thickness. This has led to the adoption of a two-layer or three-layer fluid system for studying the ISWs. However, this assumption has limited success for understanding the effects of variable pycnocline thicknesses on the wave generation and propagation. This paper discusses the broadening of pycnocline thickness on the generation of an ISW in a wave flume and its subsequent effects on wave amplitude and potential energy across a submerged trapezoidal obstacle under laboratory conditions. Three different definitions for the nominal pycnocline thickness are discussed, based on the measured fluid density profiles and the calculated buoyant frequency profiles. As the pycnocline thickness increased after repeated wave-makings, the incident ISW amplitude decreased as expected, as well as the wave speed across the obstacle. Moreover, as the thickness broadened, the fluid system appeared to contain two or multiple peaks rather than single peak when the pycnocline was thin and finite. This implies that the resultant wave might consist of several modes (at least mode-2) in the flume even at its generation stage.

Simulation of two-dimensional internal waves generated by a translating and pitching foil

A code developed on the basis of the flux-difference splitting scheme and the hybrid Cartesian/immersed boundary method is applied for two-dimensional simulation of internal waves generated by a foil that is translating and pitching simultaneously near a material interface. The interface is captured as a moving contact discontinuity without any additional treatment along the interface. An approximate Riemann solver is used to estimate numerical fluxes across the discontinuity. Immersed boundary nodes are distributed within an instantaneous fluid domain on the basis of edges crossing a boundary. Dependent variables are reconstructed at the immersed boundary nodes along local normal lines to the boundary. The present results on the propagation of internal solitary waves generated by the collapse mechanism are compared with other computational results and good agreement is found. The code is validated through comparisons with recent experimental results on the waveform inversion from depression type to elevation type during the interaction between an internal solitary wave and a trapezoidal obstacle. Internal waves generated by a translating and pitching foil are simulated. Grid independence tests of the computed results are carried out. Pairs of traveling vortices are correlated to local sinking or rising at the interface.

Experimental and numerical characterization of aerodynamic noise applied to moderate Reynolds number airflow

In the study of aerodynamic noise, a tackling challenge is to understand the underlying aeroacoustic mechanisms leading to its generation. The current paper aims at contributing to the noise characterization by focusing on moderate Reynolds number (100 ≤ Re ≤ 10000) airflow circulating through a rectangular channel containing a trapezoidal obstacle near the outlet. The outcome of large Eddy simulation and acoustic experiments are compared for different experimental boundary conditions at inlet and outlet, and for different apertures below the obstacle.

Effect of frontal slope on waveform evolution of a depression interfacial solitary wave across a trapezoidal obstacle

Waveform evolution associated with a depression interfacial solitary wave (ISW) over uniform slope or slope-shelf with different front slopes has been observed in many laboratory experiments and field studies since the 1980s, and by numerical modeling in more recent time. However, attention was mainly focused on waveform validation with KdV theory, wave run-up, reflection, energy dissipation and evolution on emergent mild uniform slope, rather on wave evolution and inversion across the plateau of a slope-shelf with steep front slopes, which are common in field conditions. Since it is often difficult to measure the entire process of waveform evolution in the field, laboratory experiments are adopted as an alternative to compliment field observations. This paper presents the results of laboratory experiments on ISW evolution across a submerged trapezoidal obstacle with four different front slopes, ranging from mild to very steep and vertical. Our results indicate that not only the likelihood of internal hydraulic jump, waveform inversion and the strength of internal wave breaking reduced, but more wave energy dissipated as well, as the front slope steepened. Upon using Hilbert–Huang transform to analyse the wave profiles recorded at four probe locations along the wave flume, the variability in the instantaneous characteristic wave period can be detected while an ISW propagated across a trapezoidal obstacle.

Assessment of the major hazard potential of interfacial solitary waves moving over a trapezoidal obstacle on a horizontal plateau

Over the last few decades, a lot of attention has been concentrated on the consequences of marine impacts, especially those caused by the tsunami wave train. Internal solitary waves are similar to the surface waves that commonly occur in the waters of the ocean or large lakes and can have significant effects on oceanic mixing, climate change, the movement of submerged plankton, and the weathering of geological structures. This motion can be severe enough to create natural hazards such as submarine tsunamis in the ocean. These could also even occur in large lakes. The present work aims to contribute to this knowledge base by studying internal wave propagation on a shallow continental shelf following a particular marine impact. A series of laboratory experiments were conducted in order to clarify the movement of an interfacial solitary wave across a uniform slope and a horizontal plateau forming a slope-shelf topography. The results obtained from test runs indicate that the wave maintains its strength, having a direct impact on the natural ecology of the local oceanic environment. Comparison with different seabed topographies is also presented to demonstrate the propagation of an internal wave over a trapezoidal barrier. A better fitting and more appropriate model is employed to examine the relationship between the physical parameters for better predicting the evolution of an internal solitary wave as it moves over a trapezoidal obstacle on a horizontal plateau.

Laboratory experiments on waveform inversion of an internal solitary wave over a slope-shelf

Internal solitary waves (ISWs) have been detected in many parts of the world oceans, particularly over slope-shelf topography, on which signature of waveform inversion has been identified. The effects of these waves on engineering operations and ecological process have also been reported in the literature. This article reports the results of a series of numerical modeling and laboratory experiments on waveform evolution of a depression ISW in a nearly stratified two-layer fluid system, in which specific water depth ratios above the horizontal plateau of the trapezoidal obstacle were arranged to facilitate the occurrence of waveform inversion. Classifications of waveform instability (no instability, shear instability and overturning with breaking) on the slope are confirmed in the present laboratory study. Numerical results for waveform variation are also found in fair agreement with the laboratory measurements for cases without waveform inversion and minor internal breaking. Moreover, laboratory results revealed that the depth ratio of the stratified two-layer fluid above the plateau and the magnitude of the incident ISW were the two most important factors for promoting waveform inversion beyond a turning point, in addition to the requirement of a sufficient distance from the shoulder of the trapezoidal obstacle. These factors also influenced the outcome of the shoaling process, energy dissipation, internal wave breaking and turbulent mixing on the front slope, as well as the likelihood of waveform inversion on the horizontal plateau. Contrary to the common perception, it was also observed, at least from the results of the present laboratory experiments, that not all the incident ISWs of depression would produce waveform inversion on the plateau, where the upper layer was physical greater than the bottom layer, unless moderate incident wave was provided. The outcome might also be attributed to the limited distance from the shoulder onto the plateau in the present laboratory setup. However, once waveform inversion occurred on the plateau, it was found, among others, that: (1) the amplitude of the transmitted leading crest and trough might be as low as 30 and 20%, respectively, to the amplitude of the incident wave in depression; (2) the characteristic wavelength of the transmitted leading trough doubled while that of the crest was asymptotically one-half of the incident wavelength, despite the wide range variation in the depth ratios above the plateau; and (3) the transmitted potential wave energy of the leading crest contained 30% of the incident energy. Based on the results of present laboratory experiments, the range for the non-dimensional parameter α, which indicates the effect of nonlinearity and the promotion of waveform inversion on horizontal plateau, will be proposed.

Laboratory experiments on depression interfacial solitary waves over a trapezoidal obstacle with horizontal plateau

While shoaling from deep water in a stratified ocean, an internal wave may encounter different types of submarine topography. As it travels, the wave may generate vortex motion on a slope, turbulent mixing between the upper and bottom layer, and even waveform inversion on the plateau of a slope-shelf feature. Although many oceanographers have believed that the inversion from depression to elevation may commence at the turning point where the upper and low layer are equal in depth, this phenomenon has not been fully verified in field observations or numerical schemes. In order to clarify this unique phenomenon, a series of laboratory experiments were conducted on the evolution of an interfacial solitary wave of depression across a slope followed by a horizontal plateau on slope-shelf obstacle. Experimental results indicate the length of the plateau may become a proxy to determine whether the inverted waveform could maintain its strength or be weakened swiftly, which could inflict direct impact on the ecology of the local oceanic environment. Comparison on the internal flow field is also presented in this paper to illustrate the process of waveform inversion as an internal wave propagating over a trapezoidal, triangular ridge and uniform long slope, respectively.

Surf zone wave overtopping a trapezoidal structure: 1-D modelling and PIV comparison

Experiments have been undertaken on surf zone waves, with a surf similarity parameter of about 0.3, overtopping a trapezoidal obstacle with 1:2 side slopes, on a beach of 1:20 slope. Particle image velocimetry (PIV) investigation has shown complex vortical structures resulting from shoreward propagating bores interacting/colliding with bores partially reflected from the obstacle, before overtopping the obstacle. A 1-D depth-averaged shallow-water model captures qualitatively much of the wave dynamics. However, the marked turbulent air entrainment in the collision zone appears significant in raising mean water level relative to the model and causing a phase lag in the model relative to the experiment. Peak overtopping levels are overpredicted by about 100% with this phase lag.

Nonlinear progressive internal gravity wave on fluid of trapezoidal bottom

In the present paper we discuss a theoretical model for the interfacial profiles of progressive nonlinear waves which result from introducing a trapezoidal obstacle, of finite height, attached to the bottom below the flow of a stratified, ideal, two layer fluid, bounded from above by a rigid boundary. Assuming a very large horizontal length compared with the vertical height allows us to apply the shallow-water approximation theory, and, consequently, a nonlinear perturbation method is presented to construct per power series the analytical solution for the interfacial profiles of the progressive waves. The dependence of the interfacial profile on the trapezoidal obstacle size, as well as its dependence on some flow parameters, such as the ratios of depths and densities of the two fluids, have been studied and illustrated.

Super-critical free-surface flow over a trapezoidal obstacle

A numerical method based on series truncation is presented to solve the problem of an irrotational, inviscid, incompressible and steady flow over a two-dimensional trapezoidal obstacle, with obstacle height W, lying on the bottom of the running stream. The suggested numerical method for the solution of the fully nonlinear problem is presented for which the flow is super-critical both upstream and downstream. It is found that solutions exist for symmetric trapezoidal for arbitrary size. The results are plotted for different trapezoidal shapes and different values of Froude number F > 1. The effect of the Froude number, the bottom height and the shape of the bottom are discussed.