Obstacle Height Research Articles

TF/TA Optimal Flight Trajectory Planning Using a Novel Regenerative Flattener Mapping Method

In this paper, a new methodology has been proposed to enhance the conformal mapping applications in the process of optimum trajectory planning in Terrain Following (TF) and Terrain Avoidance (TA) Flights. The new approach uses the conformal mapping concept as a flattener tool to transform the constrained trajectory-planning problem with flight altitude restrictions due to the presence of obstacles into a regenerated problem with no obstacle and minimal height constraints. In this regard, the Schwarz–Christoffel theorem has been utilized to incorporate the height constraints into the aircraft dynamic equations of motion. The regenerated optimal control problem then is solved employing a numerical method namely the direct Legendre-Gauss-Radau pseudospectral algorithm. A composite performance index of flight time, terrain masking, and aerodynamic control effort is optimized. Furthermore, to obtain realistic trajectories, the aircraft maximum climb and descent rates are imposed as inequality constraints in the solution algorithm. Several case studies for two-dimensional flight scenarios show the applicability of this approach in TF/TA trajectory-planning. Extensive simulations confirm the efficiency of the proposed approach and verify the feasibility of solutions satisfying all of the constraints underlying the problem

Improving the design of the trolley for the manual harvesting of strawberry

The main goal of the research is to identify the degree of influence of the asymmetry of the resistance forces on the rolling wheels of a trolley designed to relocate the picker in the strawberry garden plantation when hand picking berries on the stability of its straight-line movement. The theoretical hypothesis was formulated in relation to a three-wheeled cart, the front wheel of which is controllable and located in the central aisle, and the rear wheels - in two adjacent wheels. According to the results of calculations, with such an arrangement of the cart, ensuring the straightness of its movement only by varying the position of the reference point for the collector's leg when it is pushed away from the aisle surface is already difficult with a twofold increase in the resistance to rolling for one of the wheels. As a result of an experimental three-wheeled trolley test, it was found that when using wheels from a 700-mm diameter bike and its additional loading with ballast weighing 704,6 N, simulating the average weight of the picker, the triple difference between the wheel rolling forces occurs when an additional obstacle appears in front of one of they are only 13 mm high. When raising the height of an additional obstacle to 45 mm, the degree of differentiation between the forces of resistance to rolling wheels increased to 8,3 times. In this regard, it is advisable to supply the trolley with a device for additional manual adjustment of the process of its straight-line movement along the rows. In the experimental version of the trolley for this purpose, a lever was mounted on the axis of rotation of the front wheel fork, the free end of which was brought into a zone convenient for access by the assembler’s left hand.

GPU accelerated MPS method for large-scale 3-D violent free surface flows

In this paper, GPU acceleration technique is applied to overcome the low computational efficiency of MPS. Based on modified MPS and GPU technique, an in-house solver MPSGPU-SJTU is developed and used to simulate large-scale three dimensional (3-D) violent flow problems with over two million particles. In order to save the GPU memory, a suitable algorithm of creating neighbor particles list is adopted in GPU code. In addition, a new optimizing strategy for solving pressure Poisson equation (PPE) is proposed to reduce the storage and improve the computational efficiency. The present solver is used to simulate a benchmark test of dam-break flow with an obstacle. The performance of optimized PPE is firstly verified. Comparing the results of three spatial resolutions, the convergence of present solver is also validated. The calculated results like fluid field, impact pressure on obstacle and wave heights are in good agreements with the experimental data and the results of other numerical researches. It shows that the present solver can effectively simulate the large deformation and nonlinear fragmentation of free surface. Then, this solver is used to model another dam-break flow. A more complex violent flow with moving boundary, water entry of rigid circular cylinder, is also simulated. The calculated fluid fields agree well with the experimental images. Good agreements for the movement of cylinder are achieved to show the feasibility of MPSGPU-SJTU solver on the moving boundary problem. Furthermore, the comparisons of computation times between GPU and CPU codes are conducted in all simulations. The results show that the computation time of MPS is significantly reduced by applying GPU acceleration technique.

MIXED CONVECTION HEAT TRANSFER IN TRUNCATED CONE ENCLOSURE AS SOLAR CONTAINER WITH INTERNAL CENTERED TRIANGLE OBSTACLE

In this study, the mixed convection heat transfer of the air inside a truncated cone enclosure with aspect ratio of (0.75, 1.75, 2, 2.45 and 2.65) with centered triangle obstacle height varying by (0, 2.5, 5, 7.5, 10, 12.5 and 20 cm) and the heated wall inclination angles of (20o, 30o, 40o, 50o, 60o), the Richardson number in the range of (7 to 11) was investigated numerically. The results are addressed to automotive a suggested solar container with titled solar collector. The heat transfer from the heat source (inclined solar collector) of the enclosure walls is investigated for mixed convection as interaction of the forced convection flow between the inlet and outlet port in the bottom wall. The parameters of heat source, Reynolds number, obstacle height, enclosure aspect ratio, and left and right walls titled angles are considered in this work. The numerical simulation of the problem is carried out using commercial CFD code. The results are given in terms of the streamlines, isothermal, and the enclosure Nusselt number that characterizes the heat transfer from the heat source and from the interior fluid to the enclosure walls, respectively. The results show that the interaction of the main flow and the flow at the heated walls and the buoyancy force at the heated walls increased by using a triangular obstacle and by increasing the obstacle heights, it increased by 20% when using obstacle at position of (h=5 cm). Also, it is found that the Nu increased with increasing Re and the wall heat flux. The Nu increased with increasing Ri in the case of using (h=0 and 5 cm) but it decreased slightly in the other cases and showed that the minimum value of Nu present at a heated wall inclination of θ=50o but the maximum value at θ=30o.

Distinctive Features of Pressure Fluctuation Fields on the Surface of Steps

Parametric experimental investigations of the fields of turbulent wall pressure fluctuations on the surface of steps are performed. A considerable effect of the obstacle height on the spectral composition of the pressure fluctuations behind the leading edge is shown. The transformation of the spectral composition at different observation points is illustrated. The influence of the boundary layer thickness and the sweep angle is shown to be relatively weak. The spatial variation of the local correlation scales and the convective properties of the pressure fluctuation field on the step surface is illustrated.

Variability of crossing phase in older people with Parkinson\u2019s disease is dependent of obstacle height

Our aim was investigating variability in spatiotemporal parameters and kinetics of obstacle avoidance steps of different height obstacles in people with Parkinson’s disease (PD) and healthy older people. Twenty-eight participants have included (15 PD – stage disease: 2.1 ± 0.4 pts) and 13 healthy older people (control group). Each subject performed 10 trials of the following tasks: low obstacle, intermediate obstacle and high obstacle. The presentation order was randomized by block for each condition and participant. The spatiotemporal parameters was collected by GAITRite. An optoelectronic system (Optotrak Northern Digital Inc.) with 100 Hz of frequency was used to collect obstacle parameters. The kinect parameters (propulsion impulse and braking impulse) were acquire through two force plates (AccuGait), with a frequency of acquisition 200 Hz. Intersteps variability was calculated throughout mean values, standard deviation and coefficient of variation of two obstacle avoidance steps for each trial. PD group presented greater variability than control group on vertical and horizontal distances to the obstacle. Obstacle height did not change kinect’s parameters for both groups. The combination of task complexity (obstacle height) and disease impairments (gait alteration, loss of balance, etc) contributing for greater variability of Parkinson’s group. Besides, low obstacle and high obstacle seem to exacerbate variability of distance between obstacle and foot.

Performance analysis and test of a maize inter-row self-propelled thermal fogger chassis

In view of the difficulties in weeding and plant protection in the middle and late period of maize planting, this paper proposed a self-propelled thermal fogger chassis. According to the theoretical calculation and agronomic requirements for maize planting, the structure and working principles of the self-propelled thermal fogger chassis were introduced. On this basis, the multi-body dynamics model of chassis structure was established, and the chassis traction, steering and obstacle surmounting performances were also analyzed. Then the rationality and the feasibility of the design were verified through the furrow running test and test equipped with thermal fogger. Test results showed that, the traction performance improves with the decrease of soil deformation index and increase of cohesion, and when track pre-tensioning force was about 1000 N, the machine had a good traction performance; with the decrease of the soil deformation index and the increase of cohesive force, the stability of the single side brake turn of the chassis becomes better; on the contrary, with the increase of the tightness of the crawler, the steering radius turns smaller and the steering stability becomes worse. Under heavy clay, with the pre-tensioning of 1000 N, the machine has better steering stability and smaller turning radius. The obstacle-surmounting simulation result shows that on sandy soil road, the maximum climbing angle for the chassis is 42°, the height of vertical obstacle crossing is 170 mm and the trench width is 440 mm. The study provides a reference for the design of plant protection machinery in the middle and late stages of maize planting. Keywords: maize inter-rows, intelligent chassis, traction performance, steering performance, obstacle surmounting performance DOI: 10.25165/j.ijabe.20181105.3607 Citation: Chen L Q, Wang P P, Zhang P, Zheng Q, He J, Wang Q J. Performance analysis and test of a maize inter-row self-propelled thermal fogger chassis. Int J Agric & Biol Eng, 2018; 11(5): 100–107.

Design and Analysis of a Smart Blind Stick for Visual Impairment

For a long time, visually impaired person uses a white cane to guide their way when travel outside. The white cane has been useful for the blinds in improving their mobility but unfortunately the white cane has its limitation. One of the shortcomings of the white cane is that, it could only detect the obstacles that are within the contact ranges of the white cane. This problem sometimes could cause the blind person to be in trouble because of insufficient time to detect and warn new obstacles in front of the blind person. This research proposes a walking stick system that has two functions; to classify an obstacles height whether it is low or high and to detect a front hole. The ability to detect the height of an obstacle will help the visually impaired to either step over or avoid the obstacle. The ability to detect a hole should help the visually impaired to avoid it in time. The walking stick will use two ultrasonic sensors for the detection of obstacle height, and a laser sensor for the detection of hole. A controller will be used to monitor and analyze the data from the sensors and feedback to the user through a vibration sensor and buzzer. The algorithm to differentiate the height of obstacles is working well and it is able to differentiate high or low obstacles. The laser ranging sensor has successfully been tested for hole detection. Therefore, the walking stick with ultrasonic and laser sensors will help more visually impaired to move around much faster and feeling more safer due to improved warning system for their movement.

Preliminary Study of Obstacle Clearance and Compensatory Movements in Individuals with High Body Mass Index

This study investigated the effect of obstacles of different heights on task performance and compensatory movements of six individuals with a body mass index (BMI) ≥ 30kg/m2. Obstacle heights were increased from 36cm to 66cm in 5cm increments using a method of limits. Video-based task analysis was used to develop a conceptual model of obstacle clearance and compensatory movements in response to the postural challenge of increasing obstacle heights. Results from the task analysis were used to identify temporal and kinematic performance measures of dynamic balance and postural control. Changes in obstacle clearance performance and compensatory movements may indicate heightened fall risk and could be mitigated by accessible design and assistive support features in the environment.

Obstacle Detection with the Long Cane: Effect of Cane Tip Design and Technique Modification on Performance

The purpose of this study was to investigate the effect of cane tip design and cane technique modification on obstacle detection performance as they interact with the size, height, and position of obstacles. A repeated-measures design with block randomization was used for the study. In experiment one, participants attempted to detect obstacles with either a marshmallow tip or a bundu basher tip. In experiment two, participants were asked to detect obstacles using either the constant-contact technique or a modified constant-contact technique. As predicted, the obstacle detection rate with the bundu basher tip (M = 66.1%, SD = 7.4%) was significantly higher than that with the marshmallow tip (M = 54.6%, SD =6.8%), F(1, 11) = 24.19, p < .001, r = .83. However, contrary to our hypothesis, the obstacle detection rate with the modified constant-contact technique (M =56.0%, SD = 7.4%) was significantly lower than that with the constant-contact technique (M = 61.3%, SD = 5.2%), F(1, 13) = 6.49, p = .024, r = .58. In addition, participants detected the obstacles that were positioned at the center of their walking path (M = 61.9%, SD = 6.6%) at a significantly higher rate than those positioned slightly off to the side (M = 55.4%, SD = 7.3%), F(1, 13) =10.73, p = .006, r = .67. A bundu basher tip was more advantageous than the marshmallow tip for detecting obstacles. Given the findings of the study, cane users and orientation and mobility (O&M) specialists should consider using or recommending a bundu basher tip (or a similar tip that has an increased contact area with the walking surface), particularly when the traveling environment often presents unexpected obstacles that may trip the cane user.

Assessment of an augmented reality apparatus for the study of visually guided walking and obstacle crossing.

To walk through the cluttered natural environment requires visually guided and anticipatory adjustments to gait in advance of upcoming obstacles. However, scientific investigation of visual contributions to obstacle crossing have historically been limited by the practical issues involved with the repeated presentation of multiple obstacles upon a ground plane. This study evaluates an approach in which the perception of a 3D obstacle is generated from 2D projection onto the ground plane with perspective correction based on the subject's motion-tracked head position. The perception of depth is further reinforced with the use of stereoscopic goggles. To evaluate the validity of this approach, behavior was compared between approaches to two types of obstacles in a blocked design: physical obstacles, and the augmented reality (AR) obstacles projected upon the ground plane. In addition, obstacle height, defined in units of leg length (LL), was varied on each trial (0.15, 0.25, 0.35 LL). Approaches to ended with collision on 0.8% of trials with physical obstacles per subject, and on 1.4% trials with AR obstacles. Collisions were signaled by auditory feedback. Linear changes in the height of both AR and physical obstacles produced linear changes in maximum step height, preserving a constant clearance magnitude across changes in obstacle height. However, for AR obstacles, approach speed was slower, the crossing step peaked higher above the obstacle, and there was greater clearance between the lead toe and the obstacle. These results suggest that subjects were more cautious when approaching and stepping over AR obstacles.

Two-Dimensional Numerical Simulation of Detonation Transition with Multi-Step Reaction Model: Effects of Obstacle Height

ABSTRACTThe numerical simulations on DDT (Deflagration-to-Detonation Transition) in the two-dimensional channel with the repeated obstacles using multi-step reaction model are performed for various BR values (Blockage Ratio: the value obtained by dividing the height of the obstacles by the channel width). This research intends to find out more detailed mechanisms of the detonation transition in channels with obstacles in order to understand deeply the physical phenomena such as shock wave, turbulent flame, and local explosion caused by self-ignition. In the channel with repeated obstacles, filled with a stoichiometric premix gas of hydrogen/oxygen a small energy source near the left end of the channel is located as an initial ignition source. As a result, for BR = 0.3 and 0.45, the deflagration transits to detonation, and the flame is largely disturbed. Then the flame is accelerated by the repeated local explosions, the compression and expansion in the flow path, as well as strengthened shock wave. It is found that the onset of DDT has a different dependence on the height of obstacles. Also, even when local explosions occur, the detonation transition can fail, and for BR = 0.45 the detonation transition is delayed comparing with BR = 0.3 due to obstacles height.

Simulation of nanofluid natural convection in a U-shaped cavity equipped by a heating obstacle: Effect of cavity's aspect ratio

Abstract Research on nanofluid for heat transfer enhancement of thermal systems has received great attention owing to the lack of energy sources. In this study, fluid flow and natural convection heat transfer of Al2O3–Water or TiO2–water nanofluid inside a U-shaped cavity consist of a hot obstacle has been investigated numerically by lattice Boltzmann method (LBM). In this paper, different parameters are investigated such as Rayleigh number, the solid volume fraction of the nanoparticles, the U-shaped cavity's aspect ratio and heating obstacle's height on the flow field and heat transfer in the enclosure. The results showed that the Rayleigh number (Ra), cavity aspect ratio (AR) and obstacle's height can be affected on isotherms, streamlines and local and average Nusselt number. The average Nusselt number of the obstacle sides increased by increasing the Ra number and solid volume fraction of nanoparticles (ϕ) regardless the AR. In addition, by increasing the AR, the average Nusselt number increased. At low Ra, the effect of nanoparticles on increment of heat transfer for narrow cavities was more than wide ones.

Design and Implementation of Laser Rangefinderfor Obstacle Height Monitoring on Line of Sight of Microwave Communication Link

A laser rangefinder is a device that uses laser light to determine the distance of an object. The working principle of this laser rangefinder is that the laser beam that is emitted to the object will be reflected back to the rangefinder, and the required propagation time of laser beam will be calculated to get the distance value. In this study, a laser rangefinder system was designed to be used as monitoring of obstacle height between the line of sight of a microwave communication link using a quadcopter, which is used as a top-viewer picture taker. The quadcopter was used as a device to carry the laser rangefinder to measure the obstacle height between the location points of near-end and far-end. The obstacle height reading results were transmitted using a 5.8 GHz wireless transceiver to the monitoring location in real time. The data received were then processed to be displayed in the form of obstacle height graph as a function of the line of sight communication distance. The test results show that the implementation of laser rangefinder technology has an accuracy of more than 90%. Keywords : Line of Sight, Laser Rangefinder, Near-end and far-end, Quadcopter, Obstacle

Effects of a Fence on Pollutant Dispersion in a Boundary Layer Exposed to a Rural-to-Urban Transition

Simultaneous particle-image velocimetry and laser-induced fluorescence combined with large-eddy simulations are used to investigate the flow and pollutant dispersion behaviour in a rural-to-urban roughness transition. The urban roughness is characterized by an array of cubical obstacles in an aligned arrangement. A plane fence is added one obstacle height h upstream of the urban roughness elements, with three different fence heights considered. A smooth-wall turbulent boundary layer with a depth of 10h is used as the approaching flow, and a passive tracer is released from a uniform line source 1h upstream of the fence. A shear layer is formed at the top of the fence, which increases in strength for the higher fence cases, resulting in a deeper internal boundary layer (IBL). It is found that the mean flow for the rural-to-urban transition can be described by means of a mixing-length model provided that the transitional effects are accounted for. The mixing-length formulation for sparse urban canopies, as found in the literature, is extended to take into account the blockage effect in dense canopies. Additionally, the average mean concentration field is found to scale with the IBL depth and the bulk velocity in the IBL.

Effect of an obstacle on the depositional behaviour of turbidity currents

ABSTRACTTurbidity currents are responsible for much of the sedimentation in reservoirs. In order to control these flows, various methods such as placing an obstacle in their path have been proposed. In this study, the effect of inlet sediment concentration and obstacle height on the behaviour of turbidity currents is investigated experimentally. For this purpose, some experiments were carried out with different inlet concentrations and various obstacle heights. Velocity and concentration profiles were measured using an acoustic Doppler velocimeter. To examine the depositional behaviour of turbidity current, suspended sediment flux was calculated using velocity and concentration profiles of the current. The results indicate that increasing the obstacle height reduces the sediment flux upstream of the obstacle, and therefore more sedimentation occurs in the region. At low inlet concentrations, it was shown that the sediment flux is approximately constant along the channel and is independent of the obstacle height.

Effects of obesity and knee osteoarthritis on gait and postural stability in pre-bariatric surgery candidates

Knee osteoarthritis (OA) is the most common cause of chronic disability and is frequently comorbid with obesity. The personal burden of knee OA and obesity are substantial. Adults with knee OA with obesity demonstrate postural instability, which makes them susceptible to falls. The purpose of this study was to investigate gait and postural stability during flat ground walking and obstacle crossing in pre-bariatric surgery candidates. Forty-four adults with obesity (mean BMI = 43.35, SD = 4.33) and 30 adults without obesity (mean BMI = 23.10, SD–3.98) walked 60 feet at self-selected paces for 25 trials under five conditions: initial baseline on flat ground, crossing low (4 cm), medium (11 cm), and high (16 cm) obstacles, and final baseline on flat ground. Spatiotemporal kinematics were collected with a gait carpet (Protokinetics). During the final baseline, for adults with obesity, most parameters improved ( P s < 0.05); at the final baseline condition, participants had the fastest step times, stance times, single limb support times, and velocities. The analyses also revealed that during obstacle negotiation, participants had longer step times, slower velocity and wider step widths compared to level ground walking ( P s < 0.05). Most alterations in gait for individuals with obesity were observed during high obstacle crossing ( P s < 0.05). The findings suggest that obstacles pose a challenge beyond flat ground walking for pre-bariatric surgery candidates. Obstacle height also influenced participants’ gait. This supports the utility of examining gait in this population during tasks beyond flat ground walking.

Overcoming of high escarp by an all-wheel drive machine 8x8

In our research there has already been expressed the idea that from the point of view of overcoming big obstacles like escarpments, multi-axial all-wheel vehicles should have advantages over biaxial vehicles with 4x4 wheel arrangement. A thorough analysis of the movement process of a 8x8 wheeled vehicle on the escarpment which height exceeds the radius of the wheel is made. It was proved that such a vehicle can overcome the escarpment that almost twofold exceeds height of similar obstacles that a 4x4 wheeled vehicle overcomes.

Design and performance of a three-dimensional micromixer with curved ribs

The present work elucidates the design and performance analysis of a three-dimensional microchannel for its capability in mixing two different liquids. Present studies are based on cross-T micromixer in which obstacles are introduced in the form of three-dimensional curved ribs. The mixing efficiency, quantified by the mixing index (M), has been calculated for the present micromixer. Results are also compared with those having straight ribs and found an enhancement of about 15% in mixing efficiency for obstacles with curved surfaces. However, this superior mixing has been achieved with a lower pressure drop, which provides an added advantage not traditionally realized for passive micromixers. Moreover, extensive parametric studies are also conducted to understand the effect of several geometrical parameters that can influence the mixing which include the height of obstacles (h), number of modules (Nm), angle of inclination (θ) and size of the obstacles and also the inlet Re. However, there has been seen to have certain optimum values of some of the parameters for achieving maximum degree of mixing. The use of the curved ribs is found to provide superior mixing for a wide range of Re.

MODELLING OF THE KdV-BURGERS EQUATION SOLITARY WAVES IN DISSIPATIVE NONHOMOGENEOUS MEDIA

The work is a continuation of the research begun in previous works of the authors. At present, the theory of nonlinear waves is experiencing rapid development, and its results find numerous practical applications. One can mention the direction associated with the study of the origin and evolution of shock waves, solitary waves, kinks, periodic and quasiperiodic oscillations (for example, cnoidal waves) and many others. In this series, problems with the motion of solitons in a nonhomogeneous medium remain insufficiently studied; in this paper we consider the simplest model of such a medium: layered-inhomogeneous. The behavior of solutions of the single-wave type for the KdV-Burgers equation at various dissipative medium nonhomogeneities is considered. Various kinds of finite obstacles, as well as the transition from a dissipative medium to a free one are scrutinized. Numerical models of the solution behavior are obtained. The simulation was carried out using the Maple mathematical program through the PDETools package. The tasks considered in the paper are computationally-intensive and require a great deal of computer time. Of particular interest is the case of increasing the height of the obstacle while maintaining its width. When analyzing numerical experiments, the unexpected effect of increasing the wave height with increasing obstacle height is observed, and this may be the subject of further research. Along with this, as the height of the obstacle increases, ripples run ahead of the wave. It should be noted that in the previous work of the authors, another situation related to the appearance of a ripple was described. If, however, when the height of the obstacle remains constant, we again increase the width, then we observe an appreciable decrease in the wave amplitude, as demonstrated in the model charts. Thus, by this work of an experimental nature some new interesting properties of quasi-soliton motion are demonstrated on the basis of numerical simulation; they depend on the type and size of the dissipative obstacles.