Obstacle Height Research Articles

Obstacle Modeling and Structural Optimization of Four-Track Twin-Rocker Rescue Robot

In order to achieve the best obstacle surmounting performance of a mobile robot in the rescue environment, a four-track twin-rocker bionic rescue robot with an inner and outer concentric shaft was designed in this paper. From the viewpoint of dynamics, the motion process of the mass center of the robot when climbing steps forward and backward was studied. The maximum obstacle height of the robot was calculated. The relationship between the elevation angle of the car body, the swing angle of the rocker arm and the height of the steps was analyzed by simulation. The simulation results show that the maximum forward and reverse obstacle crossing heights were 92.99 mm and 155.82 mm, respectively. Obstacle climbing experiments of the designed robot prototype were carried out. It was found that the measured maximum height of the step was 95 mm, and the measured maximum height of the reverse obstacle was 165 mm. Finally, bionic particle swarm optimization was used to optimize the structural parameters of the rocker arm with an optimal length of 315.2 mm. The study of this paper can be referenced for the design and analysis of obstacle surmounting rescue robots with similar structures.

Does a knee joint position sense test make functional sense? Comparison to an obstacle clearance test following anterior cruciate ligament injury

ObjectivesTo evaluate knee joint position sense (JPS) among individuals with anterior cruciate ligament reconstruction (ACLR), cleared for return to sport, and investigate whether JPS errors are associated with outcomes of a functional obstacle clearance test (OC; downward vision occluded). DesignCross-sectional. SettingControlled laboratory. ParticipantsThirty-four individuals following ACLR, 23 non-athletic asymptomatic controls (CTRL), 18 athletes (ATH). Main outcome measuresabsolute error (AE) and variable error (VE) for weight-bearing knee JPS (target angles: 40°, 65°); minimal distances of the lower extremity from the obstacle (at any time and vertical clearance; two obstacle heights). ResultsLarger AE (P = 0.023) and VE (P = 0.010) were observed for CTRL compared with ACLR. CTRL also had larger OC distances for the trailing leg compared with ATH (P ≤ 0.046) and greater variability compared to both other groups (P ≤ 0.033). Moderate positive correlations (Rs ≥ 0.408, P ≤ 0.029) were observed between AE for the 40° angle and low-obstacle distances, for the injured ACLR leg. ConclusionsKnee JPS was worse in less-active individuals rather than following ACLR. Functional assessments like our OC test should complement isolated JPS tests, as they emphasize whole-body coordination and thus constitute more relevant estimations of proprioception.

An Obstacle Detection Algorithm Suitable for Complex Traffic Environment

For the task of obstacle detection in a complex traffic environment, this paper proposes a road-free space extraction and obstacle detection method based on stereo vision. The proposed method combines the advantages of the V-disparity image and the Stixel method. Firstly, the depth information and the V-disparity image are calculated according to the disparity image. Then, the free space on the road surface is calculated through the RANSAC algorithm and dynamic programming (DP) algorithm. Furthermore, a new V-disparity image and a new U-disparity image are calculated by the disparity image after removing the road surface information. Finally, the height and width of the obstacles on the road are extracted from the new V-disparity image and U-disparity image, respectively. The detection of obstacles is realized by the height and width information of obstacles. In order to verify the method, we adopted the object detection benchmarks and road detection benchmarks of the KITTI dataset for verification. In terms of the accuracy performance indicators quality, detection rate, detection accuracy, and effectiveness, the method in this paper reaches 0.820, 0.863, 0.941, and 0.900, respectively, and the time consumption is only 5.145 milliseconds. Compared with other obstacle detection methods, the detection accuracy and real-time performance in this paper are better. The experimental results show that the method has good robustness and real-time performance for obstacle detection in a complex traffic environment.

A gecko-inspired robot with CPG-based neural control for locomotion and body height adaptation

Today’s gecko-inspired robots have shown the ability of omnidirectional climbing on slopes with a low centre of mass. However, such an ability cannot efficiently cope with bumpy terrains or terrains with obstacles. In this study, we developed a gecko-inspired robot (Nyxbot) with an adaptable body height to overcome this limitation. Based on an analysis of the skeletal system and kinematics of real geckos, the adhesive mechanism and leg structure design of the robot were designed to endow it with adhesion and adjustable body height capabilities. Neural control with exteroceptive sensory feedback is utilised to realise body height adaptability while climbing on a slope. The locomotion performance and body adaptability of the robot were tested by conducting slope climbing and obstacle crossing experiments. The gecko robot can climb a 30° slope with spontaneous obstacle crossing (maximum obstacle height of 38% of the body height) and can climb even steeper slopes (up to 60°) without an obstacle or bump. Using 3D force measuring platforms for ground reaction force analysis of geckos and the robot, we show that the motions of the developed robot driven by neural control and the motions of geckos are dynamically comparable. To this end, this study provides a basis for developing climbing robots with adaptive bump/obstacle crossing on slopes towards more agile and versatile gecko-like locomotion.

Peking geckos (Gekko swinhonis) traversing upward steps: the effect of step height on the transition from horizontal to vertical locomotion.

The ability to transition between surfaces (e.g., from the ground to vertical barriers, such as walls, tree trunks, or rock surfaces) is important for the Peking gecko's (Gekko swinhonis Günther 1864) survival. However, quantitative research on gecko's kinematic performance and the effect of obstacle height during transitional locomotion remains scarce. In this study, the transitional locomotion of geckos facing different obstacle heights was assessed. Remarkably, geckos demonstrated a bimodal locomotion ability, as they could climb and jump. Climbing was more common on smaller obstacles and took longer than jumping. The jumping type depended on the obstacle height: when geckos could jump onto the obstacle, the vertical velocity increased with obstacle height; however, geckos jumped from a closer position when the obstacle height exceeded this range and would get attached to the vertical surface. A stability analysis of vertical surface landing using a collision model revealed that geckos can reduce their restraint impulse by increasing the landing angle through limb extension close to the body, consequently dissipating collision energy and reducing their horizontal and vertical velocities. The findings of this study reveal the adaptations evolved by geckos to move in their environments and may have applicability in the robotics field.

Remote Controlled Rover Using Rocker Bogie Mechanism

Abstract: The rocker-bogie suspension system has robust capabilities to deal with uneven terrain becauseof it’s distributing the payload over its six wheels uniformly. Most of the cover designs have been developed for Mars and Moon surface in order to understand the geological history of thesoil and rocks. Exploration operations need high speed and long distance traversal in a short mission period due to environmental effects, climate and communication restrictions In this research, a new suspension mechanism has been designed and its kinematic analysis results were discussed. One of the major shortcomings of current Rocker-Bogie rovers is that they areslow. In our project, we have focused on six-wheeled rocker bogie suspension system design which has advantage of linear bogie motion in protecting the whole system from getting rollovers during high- speed operations. This has greatly increased the reliability of structure on rough terrains and also enables its higher speed exploration with same obstacle height capacity as twice the diameter of wheel. The project aims to improve some basic working so that it can perform in a better way.

Numerical treatment of finite difference method for solving dam break model on a wet-dry bed with an obstacle

In this paper, we propose four different numerical methods for solving the Non-Linear Shallow Water Equations (NSWE), which are used to study dam-break flow over an obstacle. The discrete equations are formulated by applying various finite difference methods with filter involving wet-dry procedure. To validate our numerical model, several benchmark tests are carried out. Comparison of the computed results with the analytical and experiment data shows that our numerical model reproduces the flow with high accuracy. Moreover, we examine the effect of the shape and dimensions of the obstacle on downstream water height. Rectangular obstacles reduce downstream water height more significantly than triangular and trapezoidal ones. Downstream water height decreases non-linearly as obstacle height and width are increased.

Modeling Open Channel Flows of a Viscous Fluid: Critical Transition and Apparent Bottom

The Shallow Water model (SWM) provides a simplification of the Navier–Stokes model (NSM) for stratified flows over a topography when the depth of the fluid layer is small compared to the horizontal scale of the flow. Nevertheless, the application of SWM is limited to the case of slowly variable bottoms and fails in describing the fluid flow over steep obstacles. In this work, we propose to extend the applicability of SWM when the topography is no longer slowly variable with space, by replacing the topography with an “apparent bottom”. This methodology is tested for the laminar flow of a two-layer fluid over a semi-circular cylinder. Sixteen different steady configurations are investigated in order to assess the influence of the Froude number and the blocking factor corresponding to the ratio between the obstacle height and the fluid layer normal height. Here, the apparent bottom required for SWM is obtained by enforcing the liquid height profile to be the one obtained from full resolution (NSM).

RETRACTED ARTICLE: Augmentations of solar collector performance with involve of nanomaterial and perforated twisted tape

Perforated tape with obstacle was applied inside the absorber pipe filled with nanomaterial to intensify the efficiency of current solar collector. Simulations were done via ANSYS FLUENT with incorporating K–ε for turbulent flow and homogenous model for nanomaterial. To reduce the computation price, optimized size of grid has been selected and verification based on previous published data show the nice accuracy. Height of obstacle and number of revolutions were assumed as variables in simulations. Insert of turbulator makes the residence time to augment and stronger interaction with wall makes the outer wall become colder. Although the insert of tape makes convection to increase, the resistance with wall augments, too. Therefore, in current article, perforated shape of tape was utilized and to intensify the rotational velocity, obstacles over the tape were utilized. Augment of height and revolution can enhance the velocity about 4.58% and 7.04%. The temperature diminishes around 0.11% and 2.1% with elevate of N and Re.

An experimental study of aerodynamic noise from large obstructions in turbulent boundary layer flows

This paper reports an experimental study on the aerodynamic noise generated by a two-dimensional large obstacle in a turbulent boundary layer. Square and triangular obstacles with varying heights of h/δ=0.48,0.8,1.2,1.6, and 2 (where δ is the boundary layer thickness measured without the obstacle present) are tested at various flow speeds ranging from 20 to 50 m/s. The Reynolds number based on step height and free stream velocity ranged between 7500 and 79 000. A linear microphone array is arranged aside to measure the sound radiation in the spanwise direction. It is suggested that both square and triangular obstructions can lead to a broadband source with a dipole-type directivity. A consistent increase in the noise strength is observed with obstacle height and flow speed. The underlying noise source is revealed by comparing the acoustic spectra of different obstacle geometries. The low-frequency noise is contributed by the turbulence modification due to the flow impingement onto the obstacle, while the high-frequency sound is mainly caused by the diffraction of hydrodynamic pressure by the sharp leading edge.

An obstacle-avoiding and stiffness-tunable modular bionic soft robot

AbstractThe aim of this work is to design and model a novel modular bionic soft robot for crawling and crossing obstacles. The modular bionic soft robot is composed of several serial driving soft modules, each module is composed of two parallel soft actuators. By analyzing the influence of working pressure and manufacturing size on the stiffness of the modular bionic soft robot, the nonlinear variable stiffness model of the modular bionic soft robot is established. Based on this model, the spatial states and design parameters of the modular bionic soft robot are discussed when the modular bionic soft robot can pass through the obstacle. Experiments show that when the inflation air pressure of the modular bionic soft robot is 70 kPa, its speed can reach 7.89 mm/s and the height of obstacles passed by it can reach 42.8 mm. The feasibility of the proposed modular bionic soft robot and nonlinear variable stiffness model is verified by locomotion experiments.

Flexible gait transition for six wheel-legged robot with unstructured terrains

The flexibility of gait and trajectory planning with heavy payload are the main challenges for legged stable walking of hexapod robots in unstructured terrain, especially in time-varying and local terrain mutation conditions. To guarantee adaptability in unstructured terrain environment, the factors, including the obstacle height, terrain depth, and secure foothold as well as stability state, should be considered in the gait and trajectory planning. In this article, a novel gait transition hierarchical control framework based on a flexible gait planner (FGP), and gait feedback regulator (GFR) with behavior rules is proposed for the developed hexapod wheel-legged robot (BIT-6NAZA). The core of this gait planner is to select the optimal footholds and change gait types according to secure foothold and stability margin and kinematic margin of legs, and the GFR is applied to modify the foot-end trajectory of the selected gait according to the terrain feedback information to adapt to unstructured terrain. Finally, taking BIT-6NAZA robot as an example, the simulation and experiment are carried out under the proposed control framework. The co-simulation and experimental results show that the robot can modify the foot-end trajectory in dynamic unstructured terrain and obtain elastic gait in obstacle avoidance.

New application of MOL-PACT for simulating buoyancy convection of a copper-water nanofluid in a square enclosure containing an insulated obstacle

<abstract> <p>In this study, we have simulated transient and steady state free convection flow and heat transfer inside a square enclosure filled with a copper-water nanofluid of spherical shape nanoparticles following Tiwari-Das model. The cavity containing an insulated rectangular obstacle of height ranging from 0% to 50% of the cavity side-length. The vertical sides of the enclosure are kept at different temperatures, while the flat sides are assumed to be adiabatic as the obstacle. The combined method of lines/penalty-artificial compressibility technique (MOL-PACT) has been applied to solve the dimensional time dependent mathematical model after converting it into a non-dimensional structure. The combined method of lines/penalty-artificial compressibility technique is recently successfully applied to simulate free convection of MHD fluid in square enclosure with a localized heating. The extension of this promising technique for studying heat transfer of nanofluids is one of the objectives of this paper. Another objective of the study is to inspect the impact of several model parameters such as, the obstacle height, nanoparticles volume-fraction, nanoparticles radius and Rayleigh number on streamlines, temperature distribution and Nusselt number as an expression of heat transfer inside the enclosure. The results have been discussed and shown graphically. Comparisons with former results for related cases in the literature are made and reasonably good agreements are observed.</p> </abstract>

Efeitos causados por obstáculos na hidrodinâmica de correntes de turbidez: uma abordagem experimental

ABSTRACT This research aims to evaluate the effects of the presence of obstacles on turbidity currents hydrodynamics. Nine physical simulations of a poorly sorted mixture of water and coal (Cvol = 5%; D50 = 47 μm) were run in a laboratory test channel with three flow discharges (5, 10 and 15 L.min-1) in three different topographic configurations: runs without obstacles; runs with three 3 cm-high obstacles and runs with three 6 cm-high obstacles. The results showed that greater height of obstacles leads to greater blockage of the flow, causing changes on vertical profiles of velocity shape, flow regime (supercritical to subcritical), geometry and flow circulation in the zone between obstacles. Obstacle height reduction by 50% led to similar behavior of the turbidity current as the no-obstacles condition. After passing over the sequence of the obstacle, the turbidity current tended to regenerate a hydrodynamic structure comparable to the no-obstacles conditions.

Ideal planar fluid flow over a submerged obstacle: Review and extension

A classical problem in free-surface hydrodynamics concerns flow in a channel, when an obstacle is placed on the bottom. Steady-state flows exist and may adopt one of three possible configurations, depending on the fluid speed and the obstacle height; perhaps the best known has an apparently uniform flow upstream of the obstacle, followed by a semiinfinite train of downstream gravity waves. When time-dependent behaviour is taken into account, it is found that conditions upstream of the obstacle are more complicated, however, and can include a train of upstream-advancing solitons. This paper gives a critical overview of these concepts, and also presents a new semianalytical spectral method for the numerical description of unsteady behaviour. doi:10.1017/S1446181121000341

Design and Dynamic Simulation Analysis of a Wheel–Track Composite Chassis Based on RecurDyn

The traditional chassis has the problems of low trafficability and poor stability under complex and changeable unstructured conditions. Thus, a wheel rail composite chassis is proposed. The chassis had a tracked travel mechanism at the front wheels and a wheeled travel mechanism at the rear wheels. This study presents the design, theoretical analysis and dynamic simulation analysis of the chassis. The maximum values of the passability of the wheel–track composite chassis that can be passed were calculated according to the relevant parameters. Furthermore, the chassis was modeled and simulated using RecurDyn to verify whether the values were reasonable. According to different values of the terrain, slope, vertical obstacle height and trench width, the change regularity of the track tension and driving torque of the chassis were obtained. The chassis is designed to improve the vehicle’s ability to operate under complex and diverse unstructured conditions.

Effects of Tai-Chi Chuan Practice on Patterns and Stability of Lower Limb Inter-Joint Coordination During Obstructed Gait in the Elderly.

Losing balance or tripping during obstacle-crossing is one of the most frequent causes of falls in the elderly. As a low speed, low impact exercise, Tai Chi Chuan (TCC) can be promising in helping the elderly develop strategies for improved balance, inter-joint coordination, and end-point control during obstacle-crossing. This study investigates the effects of TCC training on the patterns and variability of the lower-limb inter-joint coordination during obstacle-crossing in the elderly. Fifteen older TCC practitioners and 15 healthy controls crossed obstacles of three different heights, while sagittal angles and angular velocities of the hips, knees and ankles were measured and their phase angles obtained. The continuous relative phases (CRP) of the hip-knee and knee-ankle coordination were also calculated. The standard deviations of the CRP curve points were averaged to obtain deviation phase (DP) values for the stance and swing phases. The TCC group was found to cross obstacles with increased leading and trailing toe-clearances with unaltered CRP values when the swing toe was above the obstacle. Long-term TCC training altered the patterns and magnitudes of the CRPs primarily over double-limb support and significantly reduced the variabilities of leading knee-ankle and trailing hip-knee and knee-ankle CRP curves over the crossing cycle, regardless of obstacle height. The current results suggest that long-term TCC practice was helpful for a crossing strategy with significantly increased foot-obstacle clearances and reduced variability of the way the motions of the lower limb joints are coordinated during obstacle-crossing. These benefits may be explained by the long-lasting effects of continuous practice of the slow movement patterns emphasizing between-limb transfer of body weight in TCC.

Experimental study of obstacle and bed roughness effects on behavior of turbidity current

Laboratory experiments were carried out to study the behavior of turbidity current under subcritical approach flow condition. In order to study the effects of solid obstacle and bed roughness on turbidity current, 24 experiments were conducted. Two trapezoidal macro-roughness elements with 0.01 m and 0.03 m height and three triangular obstacles with 0.1 m to 0.3 m height were used. The parameters such as front velocity, velocity profiles, body height, flow discharge, suspended load transport rate and efficiency of the obstacle were determined. It was found that under subcritical flow regime, the main portion of the turbidity current over the rough bed is controlled, if the obstacle height is 2–3 times of the body height. The growth of the front height depends on the inlet sediment concentration, the roughness elements and the obstacle height. The front velocity upstream of the obstacle over the smooth bed is independent of the obstacle height and significantly influenced by roughness elements. Simultaneous use of the bed roughness and obstacle significantly reduces the front velocity downstream of the obstacle. The flow discharge per unit width significantly decreases downstream of the obstacle. Simultaneous use of an obstacle and roughness elements decreases the flow discharge per unit width by about 90%. An obstacle with height equal to 0.75 of the initial height of the turbidity current with the smooth bed blocks about 65% of the suspended sediment. While, simultaneous use of the obstacle and the roughness elements blocks about 95% of the suspended sediment.

IDEAL PLANAR FLUID FLOW OVER A SUBMERGED OBSTACLE: REVIEW AND EXTENSION

AbstractA classical problem in free-surface hydrodynamics concerns flow in a channel, when an obstacle is placed on the bottom. Steady-state flows exist and may adopt one of three possible configurations, depending on the fluid speed and the obstacle height; perhaps the best known has an apparently uniform flow upstream of the obstacle, followed by a semiinfinite train of downstream gravity waves. When time-dependent behaviour is taken into account, it is found that conditions upstream of the obstacle are more complicated, however, and can include a train of upstream-advancing solitons. This paper gives a critical overview of these concepts, and also presents a new semianalytical spectral method for the numerical description of unsteady behaviour.

Risk probability evaluation for the effect of obstacle on CO2 leakage and dispersion indoors based on uncertainty theory

Carbon dioxide is a common gas in the chemical industry, and it is asphyxiating. A test system was established to determine the characteristics of indoor gas diffusion. The system comprised an enclosed space, gas discharge system, data acquisition system, and obstacle. CO2 gas concentration due to an indoor leak was measured, and characteristics of CO2 diffusion indoors in the presence of an obstacle were elucidated. The effects of obstacle height, obstacle width, and obstacle–leakage distance on gas diffusion were determined. An obstacle was discovered to hinder CO2 diffusion in the enclosed space. With increasing obstacle height, the gas was more likely to accumulate in front of the obstacle before spreading on the ground around the side of the obstacle. CO2 accumulation behind the obstacle was mainly due to ground accumulation rather than direct accumulation from the leakage source. However, the difference in CO2 concentration in the interior space was negligible for different obstacle heights. Obstacle width only weakly affected the concentration of CO2. Obstruction reduces the volume of space available to a gas. To minimize misjudgment, risk probability evaluation of the dense-gas leakage was proposed based on uncertainty theory. The combined standard uncertainty was calculated in specific cases, and the probability of misjudgment in risk evaluation was determined. The results provided scientific basis for early detection and rescue strategies during indoor CO2 leaks in the presence of an obstacle.