• 한국군사과학기술학회지
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• 제13권6호
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• pp.1051-1057
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• 2010

Database for the damage reference by armor piercing bullet test was established for both tube and plate specimens having a range of thickness. As the inclined angles of hit are increasing, it has been found that penetration damage diameter tends to increases accordingly in both specimen of the tube and plate, and such penetration damage diameter on the rear side becomes bigger than those on the front side. The tube specimen showed that the damage becomes bigger when central areas rather than the peripheral were hit. Through the plate test, it also has been found that the penetration ballistic limit for Al alloy is about 25.4mm and that of stainless steel about 12.7mm. From the fatigue analysis results using the database for damage reference, it has been identified whether the safety requirements of military aircraft could be met.

• 한국식품저장유통학회지
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• 제4권2호
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• pp.163-171
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• 1997

This study was undertaken to investigate changes m curve angle of Chinese cabbage blade during salting at various concentration(10, 15, 20, 25%) of salt to evaluated salting degree by curve angle during salting at 20$^{\circ}C$. Salt concentration of brine, the amount of water elution, salt penetration of the tissue(salt concentration of Chinese cabbage), weight loss and texture were investigated. Correlation relation between the above factors and curve angle were determined. The curve angles by method of holding the edge of the Chinese cabbage blade was measured. The curve angles of the mesophyll were proportional to salting time and salt concentration, but slope of line equation showed higher than that of mid-rib. The ideal method of salting evaluation by curve angle was MCA-MRC (the measuring curve angle of mid-rib C) at each concentration of salt. The results of curve angle when reached 3% salt of Chinese cabbage tissue calculated by MCA-MRC at 10, 15, 20 and 25% salting were 57$^{\circ}$, 43$^{\circ}$, 36$^{\circ}$, and 33$^{\circ}$, respectively. And salting times calculated by the same conditions were 19, 12.5, 9.1 and 4.4hours, respectively.

• 한국터널지하공간학회 논문집
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• 제16권6호
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• pp.585-597
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• 2014

본 연구에서는 받음각이 $45^{\circ}$인 경우에 대해 사각이 $0^{\circ}$와 $6^{\circ}$이고 S/d비가 1.3~12사이인 시험조건에 대해 슬림 코니컬커터를 사용하여 선형절삭시험동안 발생하는 커터작용력을 측정하였다. 각 시험조건에서 커터작용력인 연직력, 절삭력, 구동력을 측정하였고 그 측정결과의 평균값을 사용하여 분석을 실시하였다. 커터관입깊이가 깊어질수록 비에너지가 감소하였고 커터관입깊이에 따른 커터작용력의 변화는 사각이 $6^{\circ}$인 경우가 작게 나타났다. 이와 같은 결과로부터 사각이 $6^{\circ}$인 경우가 $0^{\circ}$인 경우에 비해 장비설계측면에서 효과적인 것으로 판단된다. 또한 $F_c/F_n$은 사각이 $6^{\circ}$일 때가 $0^{\circ}$인 경우에 비해 작게 나타났다. 그러나 사각이 있을 경우 구동력의 증가가 나타날 수 있으므로 이에 대한 고려가 필요하다.

• 자원환경지질
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• 제50권2호
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• pp.145-157
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• 2017

최근 집중강우로 인하여 전국적으로 산사태 및 사면붕괴 현상이 빈번히 발생하고 있다. 이러한 산지 및 비탈면에서 발생하는 자연재해에 대한 대책안 마련 및 설계 입력자료로서 지반의 강도정수(전단강도)를 도출해야만 한다. 그러나 현재 산지 및 비탈면에 접근하여 지반조사를 하기 위해서는 과다한 산림훼손과 많은 경제적인 비용 등이 요구되어진다. 따라서 본 연구에서는 현장에서 인력운반이 가능한 경량화된 소형동적콘관입시험기를 제작하여 다수의 지역에 대한 지반의 특성 및 강도정수를 산출하였다. 그리고 국내 및 외국의 소형동적콘관입시험 방법에 대해서 연구 분석하여 국내에 적합한 콘 재료와 시험방법을 제안하였으며, 대표적인 지역을 대상으로 현장에서 콘관입시험 Nc값과 표준관입시험 N값과 비교 분석하였다. 이와 더불어 직접전단시험 및 공내전단시험을 실시하여 토층심도별, 기반암별, 흙의 분류별 그리고 #200번체 통과량별로 Nc값과 전단강도와의 상관관계를 분석하였다. 특히 본 연구에서는 산지조건에서 가장 많이 분포하는 사질토를 대상으로 Nc값에 대응하는 전단강도(점착력 및 내부마찰각)와의 상관식을 제안하여 산지 토층에 대한 효율적인 지반강도정수를 산출하도록 하였다.

• 한국분무공학회지
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• 제6권2호
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• pp.9-15
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• 2001

The internal flow characteristics of a gasoline direct injector have been studied to improve fuel economy and reduce exhaust emissions. Computational Fluid Dynamics (CFD) is used to examine the internal flow of the GDI with the purpose of designing the optimum geometry of the injector. This study tests orifice length, cone angle, swirl angle, orifice diameter and needle lift. The results show that optimum sizes of the orifice length, cone angle, swirl angle, orifice diameter and needle lift are 0.8mm, $140^{\circ},\;120^{\circ},\;80mm\;and\;70{\mu}m$, respectively. The size of the lift does not affect the formation of the air core signficantly near the tip of the needle compared to the ball-type needle. The vena contracta phenomenon near the orifice inlet can be released by smoothing the edge.

• 한국분무공학회지
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• 제29권2호
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• pp.91-97
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• 2024

When investigating the droplet, spray, and impact of liquid on a solid plate, backlight imaging has been widely used to understand these phenomena. However, some previous studies have suffered from poor image quality. In this study, various combinations of image processing algorithms, such as white image correction, histogram equalization, CLAHE, Otsu's binarization, and multi-Otsu's binarization, have been applied to flash boiling spray images to enhance image quality for qualitative observation and semi-quantitative spray angle evaluation. To acquire images with high contrast for qualitative observation, applying CLAHE was effective, making small droplets and detailed shapes of the jet noticeable. However, when images were averaged to determine spray angle or penetration length based on intensity, this method induced artifact unphysical patterns, thus requiring careful consideration. Based on the algorithm proposed in this study, the spray angle variation according to injection pressure and temperature has been calculated, showing a reasonable trend.

• 대한기계학회논문집B
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• 제23권5호
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• pp.577-586
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• 1999

Two problems with jet injection through the cylindrical film cooling hole are 1) penetration of jet into mainstream rather than covering the surface at high blowing rates and 2) nonuniformity of the film cooling effectiveness in the lateral direction. Compound angle injection is employed to reduce those two problems. Compound angle injection increases the film cooling effectiveness and spreads more widely. However, there is still lift off at high blowing rates. Shaped film cooling hole is a possible means to reduce those two problems. Film cooling with the shaped hole is investigated in this study experimentally. Film cooling hole used in present study is a shaped hole with conically enlarged exit and Inlet-to-exit area ratio is 2.55. Naphthalene sublimation method has been employed to study the local heat/mass transfer coefficient and film cooling effectiveness for compound injection angles and various blowing rates around the shaped film cooling hole. Enlarged hole exit area reduces the momentum of the jet at the hole exit and prevents the penetration of injected jet into the mainstream effectively. Hence, higher and more uniform film cooling effectiveness values are obtained even at relatively high blowing rates and the film cooling jet spreads more widely with the shaped film cooling hole. And the injected jet protects the surface effectively at low blowing rates and spreads more widely with the compound angle injections than the axial injection.

• 한국지반공학회논문집
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• 제31권1호
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• pp.25-35
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• 2015

서남해안 지역의 중간조밀한 실트질모래 지반에서 버켓기초 스커트벽체의 압입저항력을 원심모형실험을 통하여 분석하였다. 압입저항력은 석션을 작용하지 않고 버켓기초를 지반에 관입시킬 때 발생하는 저항력으로서 자중관입 깊이와 직접적으로 관계된다. 스커트벽체의 주면저항력에 의한 지반의 응력증가 효과를 고려하는 방법(Houlsby and Byrne, 2005) 을 기반으로 실험 결과와 유사한 압입저항력을 산정할 수 있었다. 압입저항력 산정에 이용되는 수평토압계수, 스커트 벽체와 지반간의 경계면 마찰각 등의 주요 물성값의 산정 방법에 대하여 기술하였다. 또한, 응력증가 효과의 고려 여부와 물성값의 변화가 압입저항력 산정 결과에 미치는 영향과 실험을 통해 계측된 압입시 지반거동에 대하여 분석하였다.

• 한국농공학회논문집
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• 제65권5호
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• pp.1-11
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• 2023

Due to climate change and aging of reservoirs, damage to embankment slopes is increasing. However, the safety diagnosis of the reservoir slope is mainly conducted by visual observation, and the time and economic cost are formidable to apply soil mechanical tests and slope stability analysis. Accordingly, this study presented a predicting method for the compaction and strength characteristics of the reservoir embankment soil using a portable static cone penetration test. The predicted items consisted of dry density, cohesion, and internal friction angle, which are the main factors of slope stability analysis. Portable static cone penetration tests were performed at 19 reservoir sites, and prediction equations were constructed from the correlation between penetration resistance data and test results of soil samples. The predicted dry density and strength parameters showed a correlation with test results between R² 0.40 and 0.93, and it was found to replace the test results well when used as input data for slope stability analysis (R² 0.8134 or more, RMSE 0.0320 or less). In addition, the prediction equations for the minimum safety factor of the slope were presented using the penetration resistance and gradient. As a result of comparing the predicted safety factor with the analysis results, R² 0.5125, RMSE 0.0382 in coarse-grained soil, R² 0.4182 and RMSE 0.0628 in fine-grained soil. The results of this study can be used as a way to improve the existing slope safety diagnosis method, and are expected to be used to predict the characteristics of various soils and inspect slopes.

• 한국분무공학회지
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• 제12권1호
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• pp.11-17
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• 2007

The swirl spray for direct-injection spark-ignition (DISI) engines was investigated using a nozzle whose exit surface shape was cut with a certain tapered angle. The reason for the change in spray's characteristics at various tapered angles was explained by the data correlating the taper and flow angles. The spray tended to shift its characteristics from the symmetric to asymmetric when the tapered angle was increased; furthermore, the spray penetration and spray cone angle were also increased. When the tapered angle was greater than the $90^{\circ}$ minus flow angle, an opened hollow cone spray was formed because of the fuel impingement against the tapered surface area of the nozzle exit. This behavior indicates that the reduction in the air pressure difference between the inner and outer spray of the spray can be achieved. This behavior also promises the potential use of the tapered nozzle for the case where the independence of the spray performance from atmospheric pressure and fuel temperature is desired.