Minimum Ground Clearance Research Articles

An experimental study on base pressure behavior during bistability characterisation for a bluff body vehicle close to the ground

The present experimental investigation is concerned with the existence of Bi-stability behaviour at various ground clearances in the wake of Square Back Ahmed Body geometry (SBAB). The experiments were performed at a Reynolds number of 7.2 × 104 in a subsonic open-type wind tunnel facility. The raw readings from the pressure scanner alone were used to predict the existence of bistability character. The bistability behavior in the wake was explored in two different ways (i) The conventional base-pressure contours and pressure gradient plot, and (ii) The wavelet analysis. The minimum ground clearance for the wake to exhibit bistability was found to be 0.468H, much higher than the values determined in the previous experimental works. The discrepancy was due to relatively high turbulence intensity in the test section and experimental setup. We also found that the bi-stability switching rate was found to increase with a decrease in ground clearance. The wavelet analysis helped in determining the existence of long time-scale frequencies associated with the Bi-stability behavior.

A cross-sectional study of foot-ground clearance in healthy community dwelling Japanese cohorts aged 50, 60 and 70 years

BackgroundFalls-related injuries are particularly serious for older people, causing pain, reduced community engagement and associated medical costs. Tripping is the leading cause of falls and the current study examined whether minimum ground clearance (MFC) of the swing foot, indicating high tripping risk, would be differentiated across cohorts of healthy 50-, 60- and 70-years old community residents in Japan.MethodsA cross-sectional population comprising the three groups (50s, 60s and 70s) of 123 Konosu City residents consented to be recorded when walking on an unobstructed surface at preferred speed. Gait biomechanics was measured using high speed (100 Hz) motion capture (OptiTrack – Natural Point Inc.), including step length and width, double support, foot contact angle and MFC (swing toe height above the ground). Multivariate Analysis of Variance (MANOVA) was used to confirm ageing effects on MFC and fundamental gait parameters. Pearson’s correlations were performed to identify the relationships between mean MFC and other MFC characteristics (SD and SI), step length, step width, double support time and foot contact angle.ResultsCompared to 50s, lower step length was seen (2.69 cm and 6.15 cm) for 60s and 70s, respectively. No other statistical effects were identified for spatio-temporal parameters between the three groups. The 50s cohort MFC was also significantly higher than 60s and 70s, while step-to-step MFC variability was greater in the 70s than 50s and 60s. Pearson’s correlations demonstrated that more symmetrical gait patterns were associated with greater MFC height, as reflected in greater symmetry in step width (50s), MFC (60s) and foot contact angle (70s). In the 70s increased MFC height correlated with higher MFC variability and reduced foot contact angle.ConclusionsMFC height reduces from 60 years but more variable MFC appears later, from 70 years. While symmetrical gait was accompanied by increased MFC height, in the 70s group attempts to increase MFC height may have caused more MFC variability and lower foot contact angles, compromising foot-ground clearance. Assessments of swing foot mechanics may be a useful component of community falls prevention.

Influence of Minimum Ground Clearance on Flow and Drag for Mileage Competition Vehicle

Influence of Minimum Ground Clearance on Flow and Drag for Mileage Competition Vehicle

Lumped-Parameter and Finite Element Models of Overhead Power Line Conductors for Dynamic Thermal Rating Purposes

The steady-state approaches traditionally used to assess the capacity of overhead transmission power lines are being progressively replaced by procedures that consider the real and extremely variable weather conditions that are present along the path of the line under analysis (Dynamic Thermal Rating). Dynamic Thermal Rating (DTR) does not just estimate the temperature of the conductor in the different spans of the line, but also some mechanical quantities like their tension and sag, in order to appreciate the limitations imposed by the constraint of the minimum ground clearance. Modern DTR procedures need, therefore, proper mechanical models of the lines, in order to assess what happens both in normal and fault conditions. This paper proposes a comparison between a Finite Element Method (FEM) and a novel lumped-parameter model implemented through the Modelica language. Different realistic scenarios have been considered, like gusts of wind and the presence of ice. The outcomes of the two dynamic models have been compared to identify a trade-off between the accuracy of results and the computational time, as well as the dependency on the number of lumped masses used to model the line.

Unified Approach for the Design, Manufacture and Test of an Off-Road Rubber Tracked Ground Vehicle (TGV)

The work in this paper proposes a unified approach which involves the design, manufacture, and test an off-road rubber tracked ground vehicle for rugged terrain conditions. The proposed vehicle overall design consists of rubber tracking system, main chassis, power train and transmission system,, steering system, suspension system and the vehicle body. The design approach of the rubber tracking system can be considered new, simple, easy to manufacture and cheap compared with what is available in the literature. The dimensions of the designed rubber tracking system are of contact length of 1700 mm, track height of 850 mm, and track width of 380 mm. The overall proposed design weight of the vehicle is 14.714 kN of 3500 mm length, 2000 mm wide, 1550 mm height with minimum ground clearance of 200 mm. A 165hp Subaru gasoline engine with transmission system, suspension system, braking system, exhaust and fuel system were selected, other parts of the vehicle were designed and manufactured such as the main chassis, rubber tracking system, steering system. Finally, the vehicle was tested and after several run trials, it was performing successfully.

Verification experiment of a small obstacle avoidance considering the minimum ground clearance

Verification experiment of a small obstacle avoidance considering the minimum ground clearance

Influence of Minimum Ground Clearance on Flow and Drag for Mileage Competition Vehicle

Influence of Minimum Ground Clearance on Flow and Drag for Mileage Competition Vehicle

Design and Safety Performance Evaluation of the Riding Three-Wheeled Two-Row Soybean Reaper

Purpose: The purpose of this study was to investigate the key factors in designing a three-wheeled two-row soybean reaper (riding type) that is suitable for soybean production, and ensure worker safety by proposing optimal work conditions for the prototype of the designed machine in relation to the slope of the road. Methods: A three-wheeled two-row soybean reaper (riding type) was designed and its prototype was fabricated based on the local soybean-production approach. This approach was considered to be closely related to the prototype-designing of the cutter and the wheel driving system of the reaper. Load distribution on the wheels of the prototype, its minimum turning radius, static lateral overturning angle, tilt angle during driving, and The working and rear overturning (back flip) angle were measured. Based on the gathered information, investigations were conducted regarding optimal work conditions for the prototype. The investigations took into account driving stability and worker safety. Results: The minimum ground clearance of the prototype was 0.5 m. The blade height of the prototype was adjusted such that the cutter was operated in line with the height of the ridges. The load distribution on the prototype`s wheels was found to be 1 (front wheel: F): 1.35 (rear-left wheel: RL): 1.43 (rear-right wheel: RR). With the ratio of load distribution between the RL and RR wheels being 1: 1.05, the left-to-right lateral loads were found to be well-balanced. The minimum turning radius of the prototype was 2.0 m. Such a small turning radius was considered to be beneficial for cutting work on small-scale fields. The sliding of the prototype started at 25°, and its lateral overturning started at 39.3°. Further, the critical slope angle for the worker to drive the prototype in the direction of the contour line on an incline was found to be 12.8°, and the safe angle of slope for the cutting was measured to be less than 6°. The critical angle of slope that allowed for work was found to be 10°, at which point the prototype would overturn backward when given impact forces of 1,060 N on its front wheel. Conclusions: It was determined that farmers using the prototype would be able to work safely in most soybean production areas, provided that they complied with safe working conditions during driving and cutting.

The Electromagnetic Environmental Impact of High-Voltage Transmission Line and its Prevention Methods

This paper calculates frequency electric field intensity by the equivalent charge method, and analyzes the main factors affecting the electromagnetic environment of the 500kV Double Circuit Transmission Lines. In the same electromagnetic transmission line calculation parameters, optimization of phase sequence can effectively reduce the frequency electric field intensity; with the increase of the distance, the line frequency electric field intensity significantly reduces away from the center line within 25m. Finally, the paper obtains the phase sequence arrangement with minimal impact on the electromagnetic environment and the minimum ground clearance meeting the environmental requirements.

Analysis on the Electromagnetic Environmental Factors of 500kV Double Circuit Transmission Line

This paper calculates frequency magnetic field strength by the Ampere's law, and analyzes the main factors affecting the electromagnetic environment of the 500kV Double Circuit Transmission Lines. In the same electromagnetic transmission line calculation parameters, optimization of phase sequence can effectively reduce the frequency magnetic field strength; with the increase of the distance, the line frequency magnetic field strength significantly reduces away from the center line within 25m. Finally, the paper obtains the phase sequence arrangement with minimal impact on the electromagnetic environment and the minimum ground clearance meeting the environmental requirements.

Estimation of minimum ground clearance (MGC) using body-worn inertial sensors

Objective assessment of balance and mobility in elderly populations using body-worn sensors has recently become a prevalent theme in falls-related research. Recent research by the authors identified mean absolute-valued vertical angular velocity measured using shank mounted inertial sensors during a timed-up-and-go test as having a strong association with falls history in a group of elderly adults. This study aimed to investigate the clinical relevance of this parameter by exploring the relationship between it and minimum ground clearance (MGC) measured with an optical motion capture system. MGC is an important variable when considering trip-related falls risk. This paper also presents a method of estimating properties of MGC during walking, across a range of speeds and gait patterns, using body-worn inertial sensors. We found that mean MGC and coefficient of variation (CV) MGC are correlated with mean absolute-valued vertical angular velocity and acceleration as measured by shank or foot mounted inertial sensors. Regression models generated using inertial sensor derived variables were used to robustly estimate the mean MGC and CV MGC measured by an optical marker-tracking system. Foot-mounted sensors were found to yield slightly better results than sensors on the shank. Different walking speeds and gait patterns were not found to influence the accuracy of the models. We conclude that these findings have the potential to evaluate a walking trial using body-worn inertial sensors, which could then be used to identify individuals with increased risk of unprovoked collisions with the ground during locomotion.

Dynamic Thermal Line Loading Monitor

Operating a reliable and safe power transmission system is the goal of BPA. In doing so, BPA usually does not attain maximum transmission capacity due to continuous loading thermal limits placed on the transmission system. Thermal limit being the highest temperature at which a line conductor can be operated without violating minimum ground clearance criteria. However, lines do not instantaneously attain their thermal limits. The time it takes a conductor to reach its thermal limit can be used to BPA's advantage (Figure 1). Instead of operating a transmission system to insure that a first contingency does not cause an overload condition, BPA can operate the system at higher current levels provided the conductor's thermal response allows adequate time for manual intervention.

Design of a Large Dual – Structure Rainout Shelter1

AbstractIn locations subject to rainfall during the cropping season, a rain excluding device must be employed to impose water stress for drought studies. A rainout shelter facility that covers 0.09 ha has been constructed for plant water stress research in central Texas. The shelter consists of twin structures connected to a single drive system and linking cable. The dual structures, which move together to cover the plot, incorporate permanent side and end walls thereby completely excluding driving rain. Minimum ground clearance of the wall allows some air movement under the closed shelter. Wind loading during shelter movement is neutralized as the structures move in opposite directions. The shelter is clad with fiberglass transmitting 70% of global radiation which allows continuing energy interception by the crop when the plots are covered. Movement of the building is controlled by a tipping bucket rain gauge, a local manual switch, and through telephone answering equipment connected electronically to the drive motor. The position of the building may be checked and changed by telephone. The sheltered area is large enough for replicated experiments with a satisfactory range of treatments. Several features have contributed to the successful operation of this shelter which is larger than any described previously.

Variation in distribution of wind pressure on overhead lines

This report describes tests undertaken to ascertain to what extent lack of uniformity in the distribution of wind velocity along the front of a gust affects the total load on the towards of an overhead line. It is shown that on spans of length up to 300 ft. over level country, uniformity of distribution occurs. On larger span lengths uniformity is not maintained, measurements on a 600-ft. span showing a reduction of about 15 per cent per unit length of conductor as compared with the load on a 300-ft. span.Over level country the height of tower will increase with span length, since conductors are erected with a constant minimum ground clearance. In general, the wind speed increases with height above ground. If then the simultaneous wind-loads on a number of spans of different lengths are compared, there will be a tendency for the load on a long span to be greater than that on a short span, and it is inferred that this tendency to increase the load will very largely offset the reduction in load due to limitation in the extent of the wind gust.In the case of a long span over a valley, the measured wind load was found to be approximately equal to that calculated on the assumption of a uniform distribution of wind velocity as measured at the tower at conductor height.