• Geomechanics and Engineering
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• 제12권6호
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• pp.899-917
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• 2017

Sixty four tests were performed in a steel tank to investigate the axial responses of piles driven into organic soil prepared at two different densities using a drop hammer. Four different pile materials were used: wood, steel, smooth concrete, and rough concrete, with different length to diameter ratios. The results of the load tests showed that the shaft load capacity of rough concrete piles continuously increased with pile settlement. In contrast, the others pile types reached the ultimate shaft resistance at a settlement equal to about 10% of the pile diameter. The ratios of base to shaft capacities of the piles were found to vary with the length to diameter ratio, surface roughness, and the density of the organic soil. The ultimate unit shaft resistance of the rough concrete pile was always greater than that of other piles irrespective of soil condition and pile length. However, the ultimate base resistance of all piles was approximately close to each other.

• Geomechanics and Engineering
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• 제11권3호
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• pp.385-400
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• 2016

Bearing capacity of open-ended piles depends largely on inner frictional resistance, which is influenced by the degree of soil plugging. While a fully-plugged open-ended pile produces a bearing capacity similar to a closed-ended pile, fully coring (or unplugged) pile produces a much smaller bearing capacity. In general, open-ended piles are driven under partially-plugged mode. The formation of soil plug may depend on many factors, including wall thickness at the pile tip (or inner pile diameter), sleeve height of the thickened wall at the pile tip and relative density. In this paper, we studied the effects of wall thickness at the pile base and sleeve height of the thickened wall at the pile tip on bearing capacity using laboratory model tests. The tests were conducted on a medium dense sandy ground. The model piles with different tip thicknesses and sleeve heights of thickened wall at the pile tip were tested. The results were also discussed using the incremental filling ratio and plug length ratio, which are generally used to describe the degree of soil plugging. The results showed that the bearing capacity increases with tip thickness. The bearing capacity of piles of smaller sleeve length (e.g., ${\leq}1D$; D is pile outer diameter) was found to be dependent on the sleeve length, while it is independent on the sleeve length of greater than a 1D length. We also found that the soil plug height is dependent on wall thickness at the pile base. The results on the incremental filling ratio revealed that the thinner walled piles produce higher degree of soil plugging at greater penetration depths. The results also revealed that the soil plug height is dependent on sleeve length of up to 2D length and independent beyond a 2D length. The piles of a smaller sleeve length (e.g., ${\leq}1D$) produce higher degree of soil plugging at shallow penetration depths while the piles of a larger sleeve length (e.g., ${\geq}2D$) produce higher degree of soil plugging at greater penetration depths.

• Journal of the Korean Wood Science and Technology
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• 제45권4호
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• pp.382-398
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• 2017

This study was conducted to identify the potential of Quercus mongolica (QUM), Pinus densiflora (PID) and Pinus rigida (PIR) as a raw material for pellet production. Larix kaempferi (LAK), which has mostly been used for pellet production in Korea, was also used as a control. All specimens contained very minimal amounts of sulfur and chlorine. Ash content of LAK was the lowest, followed by PID, PIR and QUM. For the size distribution, the mass fraction between 0.42 mm and 0.25 mm was the highest in PIR. Most fuel characteristics of the produced wood pellets improved with the use of 12% moisture content (MC) particles and the increase of the ratio of length to diameter of a hole in flat-die (L/D ratio). When the MC, bulk density and durability of QUM, PID, PIR and LAK pellets was compared with the standards of the KFRI and ISO, the use of wood particles of 12% MC and flat-die with an L/D ratio of 5.00 for PID particles are suitable for high-quality pellets in the aspects of all fuel characteristics. For PIR and QUM, further work is needed to seek the optimum conditions for the production of high-quality and durable pellets.

• 한국추진공학회지
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• 제18권6호
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• pp.19-26
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• 2014

70 N급 하이드라진 추력기 개발모델의 압력 불안정 특성 고찰을 위한 지상연소시험을 수행하였다. 단일추진제급 하이드라진이 연소시험용 추진제로 선정되었고, 촉매대에는 $Ir/Al_2O_3$ 촉매를 충전하였다. 추력실 직경변화가 연소안정성에 미치는 영향을 규명하기 위해 길이직경비(L/D) 1.03, 1.13, 1.26을 갖는 하단 추력실을 시험변수로 적용한 성능평가가 수행되었다. 개발모델은 50 Hz 근처의 저주파 불안정 특성을 내재하고 있으며, L/D 증가 및 작동압력의 감소가 정체실의 압력진동을 증대시킨다는 사실이 확인되었다.

• International Journal of Aeronautical and Space Sciences
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• 제12권3호
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• pp.296-304
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• 2011

In order to design a shear coaxial injector of solid particles with water, basic experiments on a particle laden jet are necessary. The purpose of the present study is to understand the effect of particle loading ratio on the particle spray characteristics (i.e. spreading angle, distribution of particle number density, velocity profiles, and particle developing region length). Hydro-reactive Al2O3 particles with a primary particle diameter of 35~50 ${\mu}m$ are used in this experiment. An automated particle feeder was designed to supply constant particle mass flowrates. Air is used as the carrier gas. To determine the air velocity at the orifice exit, tracers (aluminum oxide, 0.5~2 ${\mu}m$ primary diameter) are also supplied by a tracer feeder. A plain orifice type injector with 3 mm diameter, and 20 mm length was adopted. Particle image velocimetry is used to measure the mean and fluctuating velocity components along the axial and radial directions.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.366-376
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• 2008

The model tests of short pile with very small pile length/diameter(L/D) were performed in this paper. Varying the pile diameter, length, and the lateral loading point, the lateral resistance and behavior of very short pile were studied in this model tests. The experimental and analytical results are as follows. The lateral ultimate resistance of short pile in sands was the maximum at the point of h/L=0.75, regardless of pile length/diameter(L/D). As the pile diameter is larger, the lateral ultimate resistance of pile with L/D=1 decreases a little and the lateral resistance increases according to the ratio of pile length/diameter. As the lateral loads are acting on the pile, the displacement of pile head is maximum at the pile top of h/L=0, but minimum at the middle point of the pile. And if the loading point is under the middle of pile, the displacement of pile head occurs oposite in the loading direction, but its magnitude is very small.

• Smart Structures and Systems
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• 제25권3호
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• pp.311-322
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• 2020

This paper studies the influence of parameters of a novel SMA helical spring energy dissipation brace on the seismic resistance of a frame structure. The force-displacement relationship of the SMA springs is established mathematically based on a multilinear constitutive model of the SMA material. Four SMA helical springs are fabricated, and the force-displacement relationship curves of the SMA springs are obtained via tension tests. A numerical dynamic model of a two-floor frame with spring energy dissipation braces is constructed and evaluated via vibration table tests. Then, two spring parameters, namely, the ratio of the helical spring diameter to the wire diameter and the pre-stretch length, are selected to investigate their influences on the seismic responses of the frame structure. The simulation results demonstrate that the optimal ratio of the helical spring diameter to the wire diameter can be found to minimize the absolute acceleration and the relative displacement of the frame structure. Meanwhile, if the pre-stretch length is assigned a suitable value, excellent vibration reduction performance can be realized. Compared with the frame structure without braces, the frames with spring braces exhibit highly satisfactory seismic resistance performance under various earthquake waves. However, it is necessary to select an SMA spring with optimal parameters for realizing optimal vibration reduction performance.

• 대한기계학회논문집B
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• 제38권4호
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• pp.321-328
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• 2014

고고도 모사를 위한 축소형 디퓨저의 비연소장 조건에서의 성능특성을 수치적으로 파악하였다. 디퓨저 입구길이를 노즐 출구직경과 비교해 0, 50, 100%로 변화 시켰고, 디퓨저 목의 길이는 2차목의 직경과 비교해 3, 5, 6, 7, 8, 12로 다양화하여 해석하고 실제 모사실험 값과 비교하였다. 그 결과 디퓨저의 입구길이가 짧아질수록 plume의 형상은 수축되었다. 또한, 디퓨저의 2차목 길이가 디퓨저 지름의 최소 8배보다 짧으면 내부에 마하디스크가 형성되어 압력의 급격한 상승을 일으킨다. 아음속 디퓨저의 길이는 설계치의 0, 50, 75, 100%로 변화시켜 유동의 변화를 관찰하였고, 길이가 짧아질수록 2차목 내부에 갑작스런 압력 상승을 야기함을 확인하였다.

• 한국산림과학회지
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• 제99권2호
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• pp.204-212
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• 2010

This study was performed in 22 unthinned Larix olgensis plantations in northeast China. Data were collected on 95 sample trees of different canopy positions and the diameter at breast height ($d_{1.3}$) ranged from 5.7 cm to 40.2 cm. The individual tree models for the prediction of vertical distribution of live crown, branch and needle biomass were built. Our study showed that the crown, branch and needle biomass distributions were most in the location of 60% crown length. These results were also parallel to previous crown studies. The cumulative relative biomass of live crown, branch and needle were fitted by the sigmoid shape curve and the fitting results were quite well. Meanwhile, we developed the crown ratio and width models. Tree height was the most important predictor for crown ratio model. A negative competition factor, ccf and bas which reflected the effect of suppression on a tree, reduced the crown ratio estimates. The height-diameter ratio was a significant predictor. The higher the height-diameter ratio, the higher crown ratio is. Diameter at breast height is the strongest predictor in crown width model. The models can be used for the planning of harvesting operations, for the selection of feasible harvesting methods, and for the estimation of nutrient removals of different harvesting practices.

• Journal of Forest and Environmental Science
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• 제39권2호
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• pp.96-104
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• 2023

The successful restoration program requires a comprehensive understanding of variables influencing seedling efficiency. Below-ground is hypothesized to have a major impact on seedling performance of species when planted in agriculture, and degraded areas with different types of mulching. This study investigated on Sg. Terla Forest Reserve in Cameron Highlands Pahang, Malaysia. In this study randomized complete block design (RCBD) was used. The excavation method was applied to study the root system development, above, and below ground biomass distributions under different types of mulching: coconut mulching (CM), oil palm mulching (OM), plastic mulching (PM) and control (CK). The root diameter, main root length, lateral root length, root coiling, and root direction toward to sun were recorded. The results in this study indicate that mulching had significant effect on root diameter, main root length, and root distributions among treatments while for lateral root length, root: shoot ratio, dry biomass distributions, and above and below ground biomass did not showed significant effect among treatments. The highest values for root diameter, lateral root length, main root length, root distributions, dry biomass distributions and above and below ground biomass were showed in CM treatments. However 75% of root coiling was observed in seedlings between treatments.