• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.264-271
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• 2007

The flow simulations around ducted-prop of tilt-duct aircraft were conducted in this study. For the investigation of aerodynamic characteristics of various configurations of duct, the axisymmetric flow calculation method combined with actuator disk model for prop were used. The rapid two-dimensional calculation and fast grid generation enable aerodynamic analysis for various duct configurations in a very short time and anticipated to active role in optimal configuration design of duct exposed to various flight modes. For the case of angle of attack or tilt angle, the three dimensional flow calculation is conducted using the three dimensional grid simply generated by just revolving the axisymmetric grid around center axis. Through the three dimensional calculation around duct, the aerodynamic effectiveness of duct as a lifting surface in airplane mode was investigated. The flow calculations around the control vane (wing) installed in the rear section of duct were conducted The aerodynamic data of wing were compared with the data of the ducts to evaluate the aerodynamic effectiveness of ducts.

• 동력기계공학회지
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• 제13권5호
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• pp.40-45
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• 2009

This article deals with the transient analysis using multi-flexible body dynamics of a trailer vehicle, which is passing a bump on the flat road. In order to investigate the transient dynamic behavior of the trailer, we developed an equivalent finite element model for the trailer and a vehicle dynamic model for the truck using multi-body dynamics. The driving condition considered here is set as the trailer vehicle passes a bump on the flat road in 7km/h. And we investigate the time histories of vertical load and deflections on connecting points between the trailer and truck during the vehicle passes a bump. Due to the dynamic load resulted from the driving condition, additional stress concentrations are found in the trailer and the suspension connecting points between the trailer and rear axles along with kingpin.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.46-51
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• 1996

The flow field around a three dimensional minivan-like body has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations on a non-orthogonal curvilinear coordinate system using second-order accurate schemes for the time derivatives, and third/second-order scheme for the spatial derivatives. The Marker-and-Cell concept is applied to efficiently solve continuity equation. The fourth -order artificial damping is added to the continuity equation for numerical stability. A H-H type multi-block grid system is generated around a three dimensional minivan-like body. Turbulent flows have been modeled by the Baldwin-Lomax turbulent model. The simulation shows three dimensional vortex-pair just behind body. And the flow separation is also observed the rear of the body. It has concluded that the results of present study properly agree with physical flow phenomena.

• International Journal of Automotive Technology
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• 제7권2호
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• pp.187-193
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• 2006

When emergency evasion during running is required, a driver sometimes causes a vehicle to drift, that is, a condition in which the rear wheels skid due to rapid steering. Under such conditions, the vehicle enters a very unstable state and often becomes uncontrollable. An unstable state of the vehicle induced by rapid steering was simulated and the effect of differential steering assistance was examined. Results indicate that, in emergency evasion while cornering and during which the vehicle begins to drift, unstable behavior like spins can be avoided by differential steering assistance and both the stability and control of the vehicle is improved remarkably. In addition, reduction of overshoot during spin evasion by the differential steering assistance has been shown to enable the vehicle to return to a state of stability in a short time in emergency evasion during straight-line running. Moreover, the effectiveness of differential steering assistance during emergency evasion was confirmed using a driving simulator.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.214-222
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• 2002

Computer simulations are widely used to analyze passenger safety in simulated traffic accidents. ATB, Articulated Total Body, is a computer simulation model developed to predict gross human body response to such dynamic environments as vehicle crashes and pilot ejections. ATB, whose code is open, has high flexibility and application capability that users can easily insert defined modules and functions. ATB is, however, inconvenient as it was coded in FORTRAN and it needs a formated input file. Moreover, it takes much time to make input files and to modify coding errors. This study aims to increase user friendliness by adding a preprocessor program, WINATB(WINdows ATB), to the conventional ATB. WINATB, programmed in Visual C＋＋ and OpenGL, uses ATB IV as a dynamic solver. The preprocessor helps users prepare input files through graphic interface and dialog box. An additional postprocessor makes the graphical presentation of simulated results. In these case of the frontal crash, the rear impact and the side impact, the simulation results obtained by WINATB and MADYMO(MAthematical Dynamic Model) are compared to validate the effectiveness of WINAIB.

• 한국공작기계학회논문집
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• 제13권6호
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• pp.94-101
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• 2004

The purpose of this raper is to assess the benefits of frequency domain fatigue analysis and compare it with more conventional time domain techniques. The multi-body dynamic analysis, FE analysis and fatigue life prediction technique are applied for the frequency domain fatigue analysis. To obtain the dynamic load history used in the frequency domain fatigue analysis, the computer simulations running over typical road Profiles are carried out by utilizing vehicle dynamic model. The fatigue life estimation for the rear suspension system of small-sized passenger car is performed by using resonance durability analysis technique, and the estimation results are compared with the conventional quasi-static durability analysis results. For the pothole simulation, the percent changes, of the fatigue life between the two durability analysis techniques don't exceed 10%. But for the Belgian road simulation because of the resonance effect, the fatigue life using the resonance durability analysis technique are much smaller estimated than the quasi-static durability analysis results.

• Journal of Biosystems Engineering
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• 제41권2호
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• pp.67-74
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• 2016

Purpose: Many tractors have adopted the horizontal control system designed to maintain the three-point mounted implements in horizontal position when they are tilted sideways. The control system rotates the implement in the opposite direction to the inclination of rear axle of the tractor. However, the current control system was found to have poor performance in accuracy and response. A new control system was therefore developed to improve the performance. Methods: The new control system was designed to get the response of the implement to be started earlier by using the tilt information from the front axle of the tractor. By this approach, the rotation of the implement can be adjusted as required to make it horizontal at the expected time, even though the response is slow. The optimal values of the control parameters for the new system were determined by computer simulation and validated by a performance test conducted with an obstacle of 120 mm height on a flat concrete surface. The performance of the control system was evaluated by the root mean square error (RMSE) of the rotation angle of the implement with respect to the actual inclination of the rear axle. Results: The new control system reduced the RMSE of the current control system by 44.6% indicating a high performance improvement. The inclination of the front axle was easily obtained from a sensor mounted on the front axle of the tractor and used as input to the new control system. Conclusions: The method of getting the response of the implement to be started earlier by utilizing the inclination information of the front axle can be applied to improve the performance of the current control system at least cost.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.1-8
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• 2017

본 연구에서는 인휠 전기구동 시스템의 장점을 바탕으로 첨단능동안전지원 기술의 일종인 적응순항제어(Adaptive Cruise Control, ACC) 알고리즘의 고도화 방안을 제시한다. 본 연구에서 대상 차량은 전륜은 엔진에 의해, 후륜은 인휠모터에 의해 구동되는 4륜 하이브리드 구동계를 갖는 것을 특징으로 하는데, 이러한 구성은 기존 내연기관 차량을 개선하여 차량의 출력을 증가시키거나 4륜 하이브리드 형태로의 변화를 용이하게 하는 장점이 있다. 본 연구에서는 이러한 차량의 구성을 바탕으로 기본 상태에서는 엔진만을 이용하여 차간거리 제어를 수행하되, 젖은 노면 등 주행 환경에서 제어오차가 커지게 되면 후륜의 인휠모터를 구동하여 제어성능을 확보할 수 있는 ACC 알고리즘을 제안한다. 제안된 ACC 알고리즘은 상기와 같은 방법으로 ACC 제어성능을 최적화함과 동시에 기존 4륜 자동차가 갖는 장점을 그대로 유지하도록 한다. 또한 본 연구에서는 고정밀 동역학 SW를 기반으로 대상 인휠모터 및 인휠 하이브리드 구동계, 해당 구동계 기반의 ACC 제어시스템을 모델링하였으며, 이를 통해 시뮬레이션 환경을 기반으로 제안된 알고리즘의 검증 결과를 제시한다.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.338-353
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• 2016

Information on the surge behaviors and stall stagnation boundaries for a nine-stage axial flow compressor are summarized on the basis of analytical data in comparison with those for a single-stage one, with attention to the pressure ratio effect. The general trends of the surge loop behaviors of the pressure-mass flow are similar for both compressors including the fact that the subharmonic surges tend to appear very near the stall stagnation boundaries. With respect to the nine-stage compressor, however, the mild loops in the subharmonic surges tend to be very small in size relative to the deep loops, and at the same time, insufficient surge recovery phenomenon, which is a kind of subharmonic surge, appears also far from the stagnation boundary for relatively short delivery flow-paths. The latter is found to be a rear-stage surge caused by unstalling and re-stalling of the rear stages with the front-stages kept in stall in the stalled condition of the whole compressor, which situation is caused by stage-wise mismatching in the bottom pressure levels of the in-stall multi-stage compressor. The fundamental information on the stall stagnation boundaries is given by a group of normalized geometrical parameters including relative delivery flow-path length, relative suction flow-path length, and sectional area-pressure ratio, and by another group of normalized frequency parameters including relative surge frequencies, modified reduced resonance frequencies, and modified reduced surge frequencies. Respective groups of the normalized parameters show very similar tendency of behaviors for the nine-stage compressor and the single-stage compressor. The modified reduced resonance frequency could be the more reasonable parameter suggesting the flow-induced oscillation nature of the surge phenomena. It could give the stall stagnation boundary in a more unified manner than the Greitzer's B parameter.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.55-63
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• 1995

The flow field around a high-speed train including cross-wind effects has been simulated. This study solves 3-D unsteady incompressible Navier-Stokes equations in the inertial frame using the iterative time marching scheme. The governing equations are differenced with 1st-order accurate backward difference scheme for the time derivatives, 3th-order accurate QUICK scheme for the convective terms and 2nd-order accurate central difference scheme for the viscous terms. The Marker-and-Cell concept was applied to efficiently solve continuity equation, which is differenced with 2nd-order accurate central difference scheme. The 4th-order artificial damping is added to the continuity equation for numerical stability. A C-H type of elliptic grid system is generated around a high-speed train including ground. The Baldwin-Lomax turbulent model was implemented to simulate the turbulent flows. To validate the present procedure, the flow around a high speed train at constant yaw angle of $45^{\circ}\;and\;90^{\circ}$ has been simulated. The simulation shows 3-D vortex generation in the lee corner. The flow separation is also observed around the rear of the train. It has concluded that the results of present study properly agree with physical flow phenomena.