• 한국군사과학기술학회지
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• 제23권5호
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• pp.502-515
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• 2020

To identify the dynamic characteristics of the Auto-leveling system applied to the Tractor-Trailer type Transporter for mounting a large scale precision equipment, Dynamics Modeling & Simulation were performed using general Dynamics Analysis Program - RecurDyn(V9R2). The axial load data, transverse load data and pad trace data of leveling actuators were obtained from M&S. And they were analyzed and compared with each other by parameters, i.e. friction coefficients on the ground, landing ram speed of actuators, and direction & quantity of ground slope. It was observed that ground contact friction coefficients affected to transverse load and pad trace; the landing ram speed of actuators to both amplitude of axial & transverse load, and this phenomena was able to explain from the frequency analysis of the axial load data; the direction of ground slope to driving sequence of landing ram of actuators. But the dynamic behaviors on the two-directional slope were very different from them on the one-directional slope and more complex.

• 공업화학
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• 제8권3호
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• pp.416-424
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• 1997

본 연구에서는 고밀집 섬유체에 의한 정적 액-액 접촉기에 대한 이론적 모델링을 통하여 섬유체 접촉기 내부에서의 물질 이동과정과 각 상에서의 축 방향 농도분포 해석이 수행되었고, 여러 운전 조건하에서 출구 농도를 예측하여 실험치와 비교하였다. 본 섬유체 액-액 추출기는 그 구조적 특성 때문에 축 방향 분산이 없는 플러그 흐름 모델로 완벽하게 묘사될 수 있었으며 data fitting을 통해 결정되어 모델식에 적용된 물질전달 계수와 섬유체 추출기 축 방향 반위 길이 당 물질전달 면적의 곱의 항인 $k_a{\sigma}$은 그 섬유체 추출기의 고유 특성 값으로 사용될 수 있었고, 그 값은 약 0.0327cm2/sec이었다.

• International Journal of Fluid Machinery and Systems
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• 제5권1호
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• pp.1-9
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• 2012

In the turbopump inducer of a liquid propellant rocket engine, cavitation is affected by acceleration that occurs during an actual launch sequence. Since cavitation instabilities such as rotating cavitations and cavitation surges are suppressed during launch, it is difficult to obtain data on the influence of acceleration on cavitation instabilities. Therefore, as a fundamental investigation, in the present study, a three-blade cyclic cascade is simulated numerically in order to investigate the influence of acceleration on time-averaged and unsteady characteristics of cavitation that arise in cascade. Several cases of acceleration in the axial direction of the cascade, including accelerations in the upstream and downstream directions, are considered. The numerical results reveal that cavity volume is suppressed in low cavitation number condition and cavitation performance increases as a result of high acceleration in the axial-downstream direction, also, the inverse tendency is observed in the axial-upstream acceleration. Then, the regions in which the individual cavitation instabilities occur shift slightly to a low-cavitation-number region as the acceleration increases downstream. In addition, in a downstream acceleration field, neither sub-synchronous rotating cavitation nor rotating-stall cavitation are observed. On the other hand, rotating-stall cavitation occurs in a relatively higher-cavitation-number region in an upstream acceleration field. Then, acceleration downstream is robust against cavitation instabilities, whereas cavitation instabilities easily occur in the case of acceleration upstream. Additionally, comparison with the Froude number under the actual launch conditions of a Japanese liquid propellant rocket reveals that the cavitation performance will not be affected by the acceleration under the current launch conditions.

• 대한기계학회논문집B
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• 제27권4호
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• pp.466-475
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• 2003

The gun-type gas burner adopted in this study is generally composed of eight slits and swirl vanes. Thus, this paper is studied to investigate the effect of slits and swirl vanes on the turbulent flow fields in the horizontal plane of gas swirl burner with a cone type baffle plate measured by using X-probe from hot-wire anemometer system. This experiment is carried out at flow rate 450 $\ell$/min in the test section of subsonic wind tunnel. The axial mean velocity component in the case of burner model with only swirl vanes shows the characteristic that spreads more remarkably toward the radial direction than axial one, it does, however, directly opposite tendency in the case of burner model with only slits. Consequently. both slits and swirl vanes composing of gun-type gas burner play an important role in decrease of the speed near slits and increase of the flow speed in the central part of a burner because the biggest speed spurted from slits encircles rotational flow by swirl vanes and it drives main flow toward the axial direction. Moreover, the turbulent intensities and turbulent kinetic energy of gun-type gas burner are distributed with a fairly bigger size within X/R<0.6410 than burner models which have only slits or swirl vanes because the rotational flow by swirl vanes and the fast jet flow by slits increase flow mixing, diffusion, and mean velocity gradient effectively.

• Korean Chemical Engineering Research
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• 제47권1호
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• pp.72-78
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• 2009

전기전도성 이방성 복합재료의 방전가공에 대하여 비정상상태 수식모델을 세우고 갤러킨의 유한요소법으로 해를 구하였다. 피삭재의 온도 분포와 분화구의 모양 및 공작물 제거 속도를 공정 매개변수에 관하여 구득하였다. 계산의 정확도와 효율을 위하여 앞선 연구에서 최적치로 선정된 $12{\times}12$ 요소의 비규칙 체눈을 사용하였다. 알루미나/티타늄 카바이드 복합재료의 물성을 재료의 물성으로 선정하였고 51.4 V의 전압과 7 A의 전류를 갖는 전력을 적용하였으며 제거 효율을 10%로 전열 이방성 계수를 2와 3으로 가정하였다. 불꽃이 일어나면서 피삭재는 즉시 녹기 시작하였고 열적 손상 영역이 형성되었다. 또한 시간이 흘러감에 따라서 분화구의 경계가 이동하는 것이 확인되었다. 반경 방향과 축 방향의 열전도도가 독립적으로 커지면 온도분포와 분화구의 모양이 각각 반경 방향과 축 방향으로 이동하였다. 공작물 제거 속도는 축 방향의 열전도도보다 반경 방향의 열전도도가 증가할 때 더욱 커지는 것으로 나타났다.

• 한국항공우주학회지
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• 제49권8호
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• pp.699-708
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• 2021

본 논문에서는 제자리 비행하는 동축반전 로터의 설계 파라미터인 상하부 로터의 축 간격에 따른 공력 특성 및 공력소음 특성에 관해 전산유체해석을 통해 분석하였다. Reynolds Averaged Navier Stokes 방정식을 사용하여 공력 해석을 진행하였으며 공력소음 해석 시에 Ffowcs Williams ans Hawkings 방정식을 사용하여 공력 특성 및 공력소음 특성을 비교하였다. 동축반전 로터는 회전에 의해 상하부 로터가 다른 각도를 가지며, 위상이 주기적으로 변하는 비정상 특성을 가진다. 상하부 로터의 간격이 증가함에 따라 유동 상호간섭이 감소하여 추력 및 토크의 공기역학적인 효율이 증가함을 확인하였다. 공력소음 관점에서 회전 평면 방향으로 방사하는 소음 특성은 축 간격에 의한 영향이 미미하게 나타났다. 로터 수직 아래 방향으로 주파수가 증가함에 따라 음압이 감쇄하지 않고 크기가 유지되어 전체 음압 수준을 증가시킨다. 동축반전 로터의 축 간격이 증가함에 따라 유동의 비정상 특성이 감소하여 전체 음압 수준이 크게 감소함을 확인하였다.

• Steel and Composite Structures
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• 제30권2호
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• pp.81-96
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• 2019

The behavior of a new Three-Tube Buckling-Restrained Brace (TTBRB) with circumference pre-stress (${\sigma}_{{\theta},pre}$) in core tube are investigated through a verified finite element model. The TTBRB is composed of one core tube and two restraining tubes. The core tube is in the middle to provide the axial stiffness, to carry the axial load and to dissipate the earthquake energy. The two restraining tubes are at inside and outside of the core tube, respectively, to restrain the global and local buckling of the core tube. Based on the yield criteria of fringe fiber, a design method for restraining tubes is proposed. The applicability of the proposed design equations are verified by TTBRBs with different radius-thickness ratios, with different gap widths between core tube and restraining tubs, and with different levels of ${\sigma}_{{\theta},pre}$. The outer and inner tubes will restrain the deformation of the core tube in radius direction, which causes circumference stress (${\sigma}_{\theta}$) in the core tube. Together with the ${\sigma}_{{\theta},pre}$ in the core tube that is applied through interference fit of the three tubes, the yield strength of the core tube in the axial direction is improved from 160 MPa to 235 MPa. Effects of gap width between the core tube and restraining tubes, and ${\sigma}_{{\theta},pre}$ on hysteretic behavior of TTBRBs are presented. Analysis results showed that the gap width and the ${\sigma}_{{\theta},pre}$ can significantly affect the hysteretic behavior of a TTBRB.

• 구강회복응용과학지
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• 제21권2호
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• pp.153-167
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• 2005

The purpose of this study was to compare the v-shape thread with the square shape thread of fixture in the view of stress distribution pattern using finite element stress analysis. The finite element model was designed with the parallel placement of two standard fixtures(4.0 mm diameter ${\times}$ 11.5 mm length) on the region of mandibular 1st and 2nd molars. Three dimensional finite element model was created with the components of the implant and surrounding bone. This study simulated loads of 200 N at the central fossa in a axial direction (load A), 200 N at the buccal offset load that is 2 mm apart from central fossa in a axial direction (load B), 200 N at the buccal offset load that was 4 mm apart from central fossa in a axial direction (load C). These forces of load A',B',C' were applied to a $15^{\circ}$ inward oblique direction at that same site with 200 N. Von Mises stress values were recorded and compared in the supporting bone, fixture, and abutment screw. The following results have been made based on this study : 1. The highest stress concentration occurred at the cervical region of the implant fixture. 2. Von Mises stress value of off-site region was higher than that of central fossa region. 3. Square shape thread type showed more even stress distribution in the vertical and oblique force than V-shape thread type. 4. Stress distribution was the most effective in the case of buccal offset load (2, 4 mm distance from central fossa) in the square shape thread type. 5. V-shape thread type revealed higher von Mises stress value than square shape thread type in all environmental condition. The results from numerical analyses concluded that square shape thread type had the lower destructive stress and more stress distribution between the fixture and bone interface than V-shape thread type. Therefore, square shape thread type was regarded as optimal thread configuration in biomechanical concepts.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.250-257
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• 2011

The power input to an infinite cylindrical shell excited by a point force is investigated. The circumferential direction and axial direction of the cylindrical shell is assumed as a two-dimensional unbounded medium, and the point force is replaced as a periodic array of imaginary sources. The spatial Fourier transform is taken from the equation of motion of the cylindrical shell, which is derived from the static model of Donell-Mushtari-Vlasov. The inverse Fourier transform is taken to derive the vibration responses. Mobility from out-of-plane forces and in-plane forces are derived from the obtained vibration responses. The theory is applied to a cylindrical shell excited by a normal direction of point force.

• 전기의세계
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• 제26권2호
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• pp.104-110
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• 1977

This paper investigates temperature distribution of plasma jets which used argon gas, and nitrogen gas mixed with argon as working fluids in spectroscopic method, and studies correlations between them main results are as follows; 1) The temperature at the center of plasma jet increases with are current and gas flow, and decreases with magnetic flux density along the axial direction. 2) The changing rate of temperature of plasma jet in the radial direction decreases rapidly beyond 2mm from central axis. 3) Temperature drop rate of plasma jet in the central axis direction appears most apparant beyond 13mm above the nozzle exit. 4) When argon gas mixed with a small amount of nitrogen, plasma temperature increases at same are current compared with the case of argon gas only.