• 대한기계학회논문집A
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• 제37권8호
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• pp.953-960
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• 2013

본 논문의 목적은 수직 또는 경사각에 대한 분절형 관통자의 관통특성을 규명하는 것이다. 분절형 관통자의 기하형상비(L/D)는 각 1.0, 0.5, 0.25 이다. 적용된 충격속도와 경사각도는 각 1.5, 2.0, 2.5 km/s 그리고 $15^{\circ}$, $30^{\circ}$, $45^{\circ}$ 이다. AUTODYN-3D code 가 분절형 관통자의 관통성능을 연구하기 위해 사용되었다. 결과는 강판에 대한 분절형 관통자의 관통성능이 해당 연속적 관통자보다 분명하게 높은 특성을 나타냈다. 2.0 km/s 의 충격 속도와 L/D 가 1 일 때, 분절형 관통자의 뛰어난 관통성능을 관찰 할 수 있다. 이 경우 분절형 관통자의 관통성능은 해당 연속적인 관통자보다 7 % 높았다. 이러한 경향은 표적체와 발사체 사이의 상호작용 때문이다. 상호작용의 정도는 표적체와 발사체의 상대속도와 입사각도, 분절형 관통자의 개수에 의존하고 있다. 따라서, 분절형 관통자의 관통 성능은 충격속도의 증가, 관통자의 개수 및 관통길이를 통해서 높일 수 있음이 확인되었다.

• 동력기계공학회지
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• 제18권6호
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• pp.186-192
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• 2014

The spray structures under the stratified and homogeneous charge condition of a gasoline direct injection were investigated in a visualized constant volume chamber. The chamber pressure was controlled from 0.1 MPa to 0.9 MPa by the high pressure nitrogen and the chamber temperatures of $25^{\circ}C$, $60^{\circ}C$ and $80^{\circ}C$ were controlled by the band type heater. The fuel, iso-octane was injected by a 6-hole injector with the pressures of 7 MPa and 12 MPa. From the experiments results, it is confirmed that at lower chamber pressure, the penetration length and spray angle are mainly affected by the chamber temperature with the vaporization of the fuel droplets and generated vortices at the end region of the spray. And at higher chamber pressure, the penetration lengths at the end of the injection were about 50~60% of that at lower chamber pressure regardless of the chamber temperature and the effect of fuel injection pressure is larger than that of the chamber temperature which results from larger penetration lengths at higher fuel injection pressure than at lower fuel injection pressure regardless of the chamber temperatures.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.367-382
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• 2019

This paper presents experimental and analytical investigations on additional fixed-end rotations resulting from the strain penetration of high-strength reinforcement in reinforced concrete (RC) beam-column connections under monotonic loading. The experimental part included the test of 18 interior beam-column connections with straight long steel bars and 24 exterior beam-column connections with hooked and headed steel bars. Rebar strains along the anchorage length were recorded at the yielding and ultimate states. Furthermore, a numerical program was developed to study the effect of strain penetration in beam-column connections. The numerical results showed good agreement with the test results. Finally, 87 simulated specimens were designed with various parameters based on the test specimens. The effect of concrete compressive strength ($f_c$), yield strength ($f_y$), diameter ($d_b$), and anchorage length ($l_{ah}$) of the reinforcement in the beam-column connection was examined through a parametric study. The results indicated that additional fixed-end rotations increased with a decrease in $f_c$ and an increase in $f_y$, $d_b$ and $l_{ah}$. Moreover, the growth rate of additional fixed-end rotations at the yielding state was faster than that at the ultimate state when high-strength steel bars were used.

• 한국전산구조공학회논문집
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• 제32권2호
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• pp.133-140
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• 2019

본 논문은 Shaped charge jet(SCJ)의 관통 과정을 유한요소해석을 통해 모사하여 제트 입사속도, 관통률 그리고 관통량 증분과 같은 물리량들을 획득하였다. 이 물리량들을 hydrodynamic 이론에 적용하여 입사 제트 속도의 효율을 분석한 결과, 입사 속도가 빠른 제트의 관통 효율은 이어지는 느린 제트에 비해 높은 것을 확인하였다. 이 효율은 hydrodynamic limit(HL) 미만인 제트인 경우 큰 폭으로 감소하였다. 한편, 시간에 따른 관통량 증분과 제트 소모량의 비교는 SCJ의 이론적인 관통현상 분석을 위해서는 길이 연장 효과를 고려해야함을 보였다.

• 한국분무공학회지
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• 제22권4호
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• pp.169-174
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• 2017

The objective of this study was to verify the experimental and numerical results of spray evolution injected from different types of the nozzle-hole geometries. Spray visualization was taken by high speed camera under the different conditions. For the simulations of spray tip penetration, turbulence, evaporation and break-up model were applied K-zeta-f, Dukowicz and Wave model, respectively. Also, the prediction accuracy of spray tip penetration was increased by varying the spray cone angle. At the same time, the results of this work were compared in terms of spray tip penetration, and SMD characteristics. The numerical results of spray evolution process and spray tip penetration showed good agreement with experimental one.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.229-234
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• 2001

The thermoacoustic refrigerator bas not only considerable possibility but also commercial usability, because it bas high reliability, lower vibration, no moving part, and can easily be constructed. In this study, the resonance characteristics of the thermoacoustic refrigerator were investigated for better performance, varying length of the resonance tube to 400mm, 500mm, 600mm, 700mm. In order to determine the optimum resonance tube length and the frequency, the $\lambda/4$ thermoacoustic engine and the similar apparatus of Wheatly type refrigerator were constructed. It was used air as a coolant. in the fifth harmonic, it was taken the highest ${\Delta}t$ that was $56.3^{\circ}C$ at 626Hz in 400mm tube with 40mm stack.

• Restorative Dentistry and Endodontics
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• 제37권1호
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• pp.24-28
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• 2012

Objectives: The aim of this study was to test the hypothesis, that the effectiveness of irrigation in removing smear layer in the apical third of root canal system is dependent on the depth of placement of the irrigation needle into the root canal and the enlargement size of the canal. Materials and Methods: Eighty sound human lower incisors were divided into eight groups according to the enlargement size (#25, #30, #35 and #40) and the needle penetration depth (3 mm from working length, WL-3 mm and 9 mm from working length, WL-9 mm). Each canal was enlarged to working length with Profile.06 Rotary Ni-Ti files and irrigated with 5.25% NaOCl. Then, each canal received a final irrigation with 3 mL of 3% EDTA for 4 min, followed by 5 mL of 5.25% NaOCl at different level (WL-3 mm and WL-9 mm) from working length. Each specimen was prepared for the scanning electron microscope (SEM). Photographs of the 3mm area from the apical constriction of each canal with a magnification of ${\times}250$, ${\times}500$, ${\times}1,000$, ${\times}2,500$ were taken for the final evaluation. Results: Removal of smear layer in WL-3 mm group showed a significantly different effect when the canal was enlarged to larger than #30. There was a significant difference in removing apical smear layer between the needle penetration depth of WL-3 mm and WL-9 mm. Conclusions: Removal of smear layer from the apical portion of root canals was effectively accomplished with apical instrumentation to #35/40 06 taper file and 3 mm needle penetration from the working length.

• 한국안전학회지
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• 제11권4호
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• pp.3-9
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• 1996

In this study, comparison of theoretical solutions with experimental results is examined through fracture conditions for the case of float glasses subjected static loading. The range of fracture generation limits and critical penetration energies are solved according to the impactor mass under the high velocity, and analytical method of fracture strength and penetration strength are presented. Also, fracture patterns are investigated according to impact velocities. The results obtained from this study are as follows ; 1) Radial cracks are generated from the loading point regardless of plate thickness in the case of the plate subjected to the static loading. In the case of high-speed impact, dimensions of ring cracks become to smaller and length of radial cracks becomes shorter with the rapidity of impact velocity. 2) Kinetic change volume of collision after/before is constant regardless of velocities over the range of critical penetration velocity. 3) Although the same impact energy is working, the critical penetration energy is increased with the shorter of impactor mass. 4) Although the same impact energy is working, the penetration fracture of lighter Impactor mass is generated more than that of heavier impactor mass, and the impulse of lighter impacter mass appear more than that of heavier impactor mass. Therefore, the penetration fracture in the case of greater impulse is generated earlier regardless of the of the dimensions of Impact loading.

• 대한토목학회논문집
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• 제41권2호
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• pp.133-141
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• 2021

프로브 차량 데이터로부터 전수화 된 교통량, 밀도, 대기행렬 길이를 추정하기 위해 프로브 차량 비율이 필요하다. 이를 위해 기존 연구는 프로브차량과 일반 차량의 위치에 대한 확률구조를 활용하여 지점 검지기 없이 프로브 차량 비율을 추정하는 방법을 제시하였으나, 기존 연구의 방법론은 다차로 도로에 적용할 수 없다는 한계가 있었다. 따라서 본 연구는 각 차로의 대기행렬 길이에 확률분포를 도입함으로써 다차로 접근로에서 프로브 차량 비율을 추정하고자 하였다. 사례연구 결과, 추정치와 관측치 간 이격이 있었으나, 추정치가 관측치의 경향을 따라가는 것으로 나타났으며, 향후 보정계수 도입 등을 통하여 추정치를 개선할 여지가 있었다. 본 연구는 지점 검지기가 없는 다차로 접근로에서 전수화 된 교통량, 밀도, 대기행렬 길이를 추정하기 위한 기초연구로서 활용될 것으로 기대된다.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.51-57
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• 1999

In this study, one side fillet welded T-joint, used in box type girder and other welding structure, was investigated by stress analysis and bending fatigue test without edge preparation, with variation of joint shape. The purpose of this study is to give the welding condiltion and design standard on manufacturing one side fillet welded T-joint. As a result, the following conclusions were obtained. 1) In one side fillet welded T-joint, the larger the leg length and the penetration depth, the greater the bending fatigue strength because reduction of stress and strain on toe and root. The increase of the longitudinal leg length rather than vertical leg length contributed to the increase in bending fatigue strength. 2) In one side fillet welded T-joint without edge preparation, both general manual welding and general automatic welding were carried out with same condition. In this case, automatic welding showed deeper penetration and more increased longitudinal leg length than manual welding, so that automatic welding offers greater bending fatigue strength. 3) For one side fillet welded T-joint without edge preparation with automatic welding, the ratio(h/t) of the leg length(h) and the main plate thickness(t) in which toe crake can occur was 1.0 over.