• Advances in aircraft and spacecraft science
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• v.4 no.6
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• pp.651-677
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• 2017

For the past ten years' efforts have been made to introduce environmentally-friendly "green" electric-taxi and maneuvering airplane systems. The stated purpose of e-taxi systems is to reduce the taxiing fuel expenses, expedite pushback procedures, reduce gate congestion, reduce ground crew involvement, and reduce noise and air pollution levels at large airports. Airplane-based autonomous traction electric motors receive power from airplane's APU(s) possibly supplemented by onboard batteries. Using additional battery energy storages ads significant inert weight. Systems utilizing nose-gear traction alone are often traction-limited posing serious dispatch problems that could disrupt airport operations. Existing APU capacities are insufficient to deliver power for tractive taxiing while also providing for power off-takes. In order to perform comparative and objective analysis of taxi tractive requirements a "standard" taxiing cycle has been proposed. An analysis of reasonably expected tractive resistances has to account for steepest taxiway and runway slopes, taxiing into strong headwind, minimum required coasting speeds, and minimum acceptable acceleration requirements due to runway incursions issues. A mathematical model of tractive resistances was developed and was tested using six different production airplanes all at the maximum taxi/ramp weights. The model estimates the tractive force, energy, average and peak power requirements. It has been estimated that required maximum net tractive force should be 10% to 15% of the taxi weight for safe and expeditious airport movements. Hence, airplanes can be dispatched to move independently if the operational tractive taxi coefficient is 0.1 or higher.

• Journal of Convergence for Information Technology
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• v.10 no.7
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• pp.153-159
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• 2020

In order to find out the condition of flow in sewer pipes, this study investigated the characteristics of tractive force of sewage flow estimated using actual measured values of water level, velocity, and flowrate in sewers located at uppermost portion in a treatment area during dry weather periods. When the scene of sewage flow was taken by CCTV after cohesive and non-cohesive solids (tofu and sand) were put on the sewer invert, it was found that the solids could be flushed without significant interruption. In sewer with slope of 0.00319, the frequency exceeding the minimum tractive force of sewage during a weekday was zero, while it was 10 per day with slope of 0.00603. During the week of the field observation, the event to exceed the minimum tractive force occurred once, suggesting that sewer odor would potentially increase. Maximum tractive force in sewer with steep slope was 2.9-3.1 N/㎡, but with gentle slope it decreased to 1.6-1.7N/㎡. It was also observed that the interval of time maintained below the criterion of minimum tractive force increased, during weekends compared to weekdays and for the sewage including non-cohesive particles which could enter combined sewers during a storm period. This study found that the sewer sediments formed by direct feces input into sewers, through sewer pipes which were designed meeting the standard sewer design criteria, could be flushed without staying as deposited solids state for a long time.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.122-130
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• 2016

The past few decades of industrialization enabled human-centered stream developments, which in turn resulted in constructing straight or covered streams, which are used only for sewage disposal purpose. However, these types of streams have become the cause of flood damages such as localized heavy rain. In response, various construction methods have been implemented to prevent stream and embankment damages. However, regulations regarding these measures only lay out minimum standards such as the height of slopes and the minimum angle of inclination. Moreover, examination of tractive force, the most crucial factor in preventing flood damage, is nonexistent. Therefore, this study evaluates various tractive forces by implementing a porous concrete tetrapod at a full scale artificial stream for experiment, controlling the rate of inflow, and measuring the velocity and depth of the stream under different experiment conditions. The test results of the compressive strength, and porosity and density of rock of the porous concrete tetrapod was between 16.6 and 23.2 MPa, and the actual measurement of air void was 10.1%, thus satisfying domestic standard. The result of tractive force experiment showed a limiting tractive force of $47.202N/m^2$, not satisfying the tractive force scope of $67N/m^2$ the stream design working expertise proposes. However, there was neither damage nor loss of blocks and hardpan. Based on previous researches, it can be expected that there will be resistance against a stronger tractive force. Therefore, it is necessary to conduct another experiment on practical limiting tractive force by adjusting some experimental conditions.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.2
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• pp.121-129
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• 2019

If sewage flows for an extended time at low velocities, solids may be deposited in the sewer. Sufficient velocity or tractive force should be developed regularly to flush out any solids that may have been deposited during low flow periods. This study aims to evaluate the periods (T) during which sewage flow greater than the minimum tractive force maintains on a spot in sewer pipe system with lower tractive force or lower velocity than expected in the design step, when a storage tank installed in a place upsteam pours water into the sewer. The effect to T of design factors of storage tank and sewer pipes was evaluated assuming the uniform flow in sewers. When the area of orifice in the storage tank is $0.062m^2$(or 0.28 m diameter), the maximum T of 31sec was maintained using the usually used preset range of values of several design factors. As the horizontal cross section of storage tank and water depth of storage tank and roughness in sewers increase, T linearly increases. Also, T linearly decreases as the diameter of a sewer pipe increases. Although T gradually decreases as the sewer pipe slope decreases to around 0.005, T decreases sharply when the slope is less than 0.003.

• Journal of Biosystems Engineering
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• v.27 no.6
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• pp.491-500
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• 2002

This study was carried out to investigate experimentally the effect of the tire inflation pressure of a tractor on soil compaction and tractive performance. Two kinds of field experiments were conducted using an agricultural tractor. One experiment is concerned with the tractive performance of the tractor at the three levels of tire inflation pressure; 50kpa, 100kpa and 200kpa, and the other one is about the soil compaction at the four levels of tire inflation pressure; 50kpa, 100kpa, 150kpa and 200kpa, at three different numbers of passes; 1, 3 and 5 passes. From the results of the field experiment, it was found that decreasing the tire inflation pressure decreased the motion resistance of tractor and increased the tractive force and tractive efficiency. The tractive and working performance of the tractor could be improved by the reduction of tire inflation pressure. Increasing the inflation pressure and the number of passes increased the soil compaction. Rate of compaction increased rapidly at the first pass and declined at subsequent passes. To reduce the effect of soil compaction for the whole field, it is recommended that tractor should follow the rut of the first pass from the subsequent passes, and decrease the inflation pressure of the driving tires up to allowable minimum level.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.6
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• pp.779-788
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• 2009

This study is the result of a field survey of four sewer networks selected from in domestic sanitary sewers. The main purpose of this study is to understand the characteristics of sediment in domestic sanitary sewers and to verify sewer design criteria using minimum Shear Stess for preventing sedimnet. This investigation was carried out at a total of 22 points in the four areas. The characteristics of the sanitary solids that were sampled for suspended solids and bedload matter showed a specific gravity of 1.09, a median particle size of 1.26mm, and 88.9% organic contents. On the other hand, deposited sediment was found at 6 points out of the 22 monitoring points. The analysis results of disposed sediment showed a specific gravity of 2.16, a median particle size of 1.31mm, and 15% organic contents. In flow velocity, the majority of deposited sites have under 0.6m/s. However, one-site which was in large-diameter collector sewers, has recorded over 0.6m/s. The analysis results of tractive force showed that the ability of tractive force has to be $1.5{\sim}2.0N/m^2$ to prevent sediment in domestic Sanitary sewers. In conclusion, to prevent sediment it is necessary to apply a design velocity criteria higher than 0.6m/s in the large diameter collector sewer.

• Geomechanics and Engineering
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• v.25 no.1
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• pp.49-58
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• 2021

The resistance of soil to the tractive force of flowing water is one of the essential parameters for the stability of the soil when directly exposed to the movement of water such as in rivers and ocean beds. Biopolymers, which are new to sustainable geotechnical engineering practices, are known to enhance the mechanical properties of soil. This study addresses the surface erosion resistance of river-sand treated with several biopolymers that originated from micro-organisms, plants, and dairy products. We used a state-of-the-art erosion function apparatus with P-wave reflection monitoring. Experimental results have shown that biopolymers significantly improve the erosion resistance of soil surfaces. Specifically, the critical shear stress (i.e., the minimum shear stress needed to detach individual soil grains) of biopolymer-treated soils increased by 2 to 500 times. The erodibility coefficient (i.e., the rate of increase in erodibility as the shear stress increases) decreased following biopolymer treatment from 1 × 10-2 to 1 × 10-6 times compared to that of untreated river-sands. The scour prediction calculated using the SRICOS-EFA program has shown that a height of 14 m of an untreated surface is eroded during the ten years flow of the Nakdong River, while biopolymer treatment reduced this height to less than 2.5 m. The result of this study has demonstrated the possibility of cross-linked biopolymers for river-bed stabilization agents.

• Journal of Navigation and Port Research
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• v.43 no.1
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• pp.9-15
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• 2019

Mooring bollards are the mandatory facility in ports for they are the objects used to fasten the ship to its position at the berth. All the mooring bollards were installed following suggested sizes, numbers, materials and shape of installation according to Port and Fishing Design Standards. However, Korea has no management standard for use of mooring bollards to safety in ship berthing. In this research, the installation standard for mooring bollards including the holding power applied to mooring bollards in berthing was studied. Also, the performance of mooring bollards for minimum safety guarantee in berthing based on research of various specification by their sizes was analyzed. The analysis on mooring bollards was examined by each power on mooring bollards from the applied force in berthing divided into horizontal and vertical direction in order to examine the performance of domestic mooring bollards, the limit force is calculated based on detailed specification research result. As a result, the working stress according to the towing force was found to be at least 150Mpa and it was evaluated to be 60% of the limit strength. Also, by comparing each forces, the appropriateness was examined and the specification of maximum capability calculated. This performance evaluation method based on detail specification of mooring bollards will be expected to be useful to examine the appropriateness of mooring bollards for various types of vessel in berthing and to develop maintenance and management standard through the performance change evaluation referring to mooring bollard detailed specification changes.