• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.59-63
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• 2005

본 연구는 재순환 유동이 램제트 연소실 슬롯 막냉각에 미치는 영향에 대하여 실험을 수행하였다. 경사진 확장면에 설치된 돌출부를 가진 냉각유로에 의해 발생된 재순환 유동이 다단 슬롯 중 첫 번째 슬롯에 영향을 미치도록 실험 장치를 구성하여, 슬롯 출구 하류에서 속도장, 온도장 및 단열 막 냉각 효율을 측정하였다 슬롯을 통해 분사된 냉각유체는 재순환 유동간의 높은 전단력과 난류강도로 인해 분사 직후 급격히 혼합되어, 냉각 성능이 감소함을 결과를 통해 확인하였다.

• Wind and Structures
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• 제9권2호
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• pp.95-108
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• 2006

Wind turbines are highly complex structures for numerical flow simulation. They normally comprise of a turbine mounted on a tower thus the movement of the turbine blades and the blade/tower interaction must be captured. In addition the ground effect should also be included. There are many more important features of wind turbines and it is difficult to include all of them. A simplified set of features is chosen here for both the turbine and the tower to show how the method can begin to identify the main points connected with wind turbine wake generation and tip vortex tower interaction. An approach to modelling the rotating blades of a turbine is proposed here. The model uses point forces based on blade element theory to model the blades and takes into account their time dependent motion. This means that local instantaneous velocities can be used as a basis for the blade element theory. The model is incorporated into a large eddy simulation code and, although many important features are left out of the model, the velocity/power performance relation is generally of the correct order of magnitude. Suggested improvements to the method are discussed.

• 대한물리치료과학회지
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• 제9권2호
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• pp.133-141
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• 2002

This purpose of this study was to design the effect of recovering of a hand amputees by Myoelectronic hand. It was designed with 2 degree of freedom in the laboratory. Myoelectronic hand had only one degree of freedom and one movement until now. Also this myoelectronic hand had multi-joint and it could move widely. Wire was used in transmission. Myoelectronic hand data was obtained by analyzing hand anatomically and measuring and that data was applied when it was designed. PID controller of Myoelectronic hand was used to it. Displacement control was applied the first link. Experiment was accomplished in Tip grasp, Power grasp and Hook grasp modes. Displacement control was good in low frequency. Velocity control was applied to each mode. The objective of the study was to develop more better multifunction myoelectronic control strategies. A myoelectronic hand with a hand amputees could do some jobs such as grasping materials, lifting weighting, holding cup and etc. As a result of this study, all subjects with hand amputees significantly improved in ADL. Further studies were needed to evaluate the effect of a myoelectronic hand with more precise laboratory equipment.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제22회 KOSCI SYMPOSIUM 논문집
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• pp.9-16
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• 2001

When large size nozzle with low jet velocity is used, the buoyancy effect arises from the density difference among propane, air, and burnt gas. Flame characteristics in such buoyant jets have been investigated numerically to elucidate the effect of buoyancy on lifted flames. It has been demonstrated that the cold jet has circular cone shape since upwardly injected propane jet decelerates and forms stagnation region. In contrast to the cold flow, the reacting flow with a lifted flame has no stagnation region by the buoyancy force induced from the burnt gas. To further illustrate the buoyancy effect on lifted flames, the reacting flow with buoyancy is compared with non-buoyant reacting flow. Non-buoyant flame is stabilized at much lower height than the buoyant flame. At a certain range of fuel jet velocities and fuel dilutions. an oscillating flame is demonstrated numerically showing that the height of flame base and tip vary during one cycle of oscillation. Under the same condition. non-buoyant flame exhibits only steady lifted flames. This confirms the buoyancy effect on the mechanism of lifted flame oscillation.

• Journal of Welding and Joining
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• 제13권4호
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• pp.122-131
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• 1995

An automatic welding equipment for thick plates requires the capability of the seam tracking of the weld line which often includes misalignment of the workpiece and variation of groove width. In this study, an automatic welding equipment and control algorithms based on the arc sensor were proposed for the GMA welding of thick plates which had misalignment and gap variation. The developed system being constituted with 5 axis can be automatically controlled by computer and also automnatically set the welding conditions such as welding current, and voltage. The proposed algorithms for the seam tracking in multi-pass welding of the thick plates were constituted as follows : the detection of weaving-end point for findng the variation of groove width, the control of welding velocity for acquiring a constant thickness deposition of weld metal, and the calculation of groove width and height of an arbitrary pass in the multi-pass weld. As results of the application of the system, it was revealed that the system had a good capability in seam tracking and made an excellent weld quality in V groove butt joint.

• Wind and Structures
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• 제22권1호
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• pp.65-87
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• 2016

The wind velocity profile over the height of a structure in high intensity wind (HIW) events, such as downbursts, differs from that associated with atmospheric boundary layer (ABL) winds. Current design codes for lattice transmission structures contain only limited advice on the treatment of HIW effects, and structural design is carried out using wind load profiles and response factors derived for ABL winds. The present study assesses the load-deformation curve (capacity curve) of a transmission tower under modeled downburst wind loading, and compares it with that obtained for an ABL wind loading profile. The analysis considers nonlinear inelastic response under simulated downburst wind fields. The capacity curve is represented using the relationship between the base shear and the maximum tip displacement. The results indicate that the capacity curve remains relatively consistent between different downburst scenarios and an ABL loading profile. The use of the capacity curve avoids the difficulty associated with defining a reference wind speed and corresponding wind profile that are adequate and applicable for downburst and ABL winds, thereby allowing a direct comparison of response under synoptic and downburst events. Uncertainty propagation analysis is carried out to evaluate the tower capacity by considering the uncertainty in material properties and geometric variables. The results indicated the coefficient of variation of the tower capacity is small compared to those associated with extreme wind speeds.

• 천문학회보
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• 제39권2호
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• pp.68.1-68.1
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• 2014

M74 is a nearby face-on spiral galaxy that hosts three core-collapse supernovae (SNe) : SN Ic 2002ap, SN II-P 2003gd, and SN II-P 2013ej. Therefore it is an ideal target to investigate the properties of the core-collapse SNe and to improve the calibration of Type II-P SNe as a standardizable candle. However, its distance is not well known. We present a new distance estimate to M74 based on the tip of the red giant branch (TRGB). From the photometry of archival F555W and F814W images taken with the Hubble Space Telescope, we derive the TRGB to be at $ITRGB=26.13{\pm}0.02$ and the distance modulus to be $30.04{\pm}0.04$ (random) ${\pm}0.12$ (systematic) (corresponding to a linear distance, $10.19{\pm}0.14{\pm}0.56Mpc$). With this result, we calibrate the standardized candle method of SNe II-P. From the absolute magnitude of SN 2003gd corrected for its expansion velocity and reddening, we derive the value of the Hubble constant, $H0=72{\pm}6{\pm}7km\;s-1\;Mpc-1$. It is in agreement with the uncertainty with the recent estimates based on the luminosity calibration of Type Ia SNe.

• 대한기계학회논문집
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• 제12권3호
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• pp.534-540
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• 1988

본 연구에서는 디이젤분무 주위기체의 유동특성중에서 유동속도에 관하여 보 고 하였다. 본모에서는 분무기간중 분사압력의 시간경과특성이 상이한 두 종류의 분 사계를 사용하여 생성된 분무와 주위 기체와의 유동방향의 시간경과 및 유입시기, 정 상유입속도 도달시간등을 분무의 축방향과 반경방향에 대하여 상세한 측정결과를 얻었 기에 보고한다.

• Journal of Mechanical Science and Technology
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• 제16권3호
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• pp.386-394
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• 2002

The present work is aimed at investigating an unusual variation in flow and performance characteristics of a small propeller fan at low flow rates. A performance test of the fan showed dual performance characteristics, i.e., radial type characteristics at low flow rates and axial type at high flow rates. Dual performance characteristics of the fan are numerically investigated using viscous flow calculations. The Finite Volume Method is used to solve the continuity and Navier-Stokes equations in the flow domain around a fan. The performance parameters and the circumferentially averaged velocity components obtained from the calculations are compared with the experimental results. Numerical values of the performance parameters show good agreement with the measured values. The calculation simulates the steep variations of performance parameters at low flow rates and shows the difference in the flow structure between high and low flow rates. At a low flow coefficient of $\Phi$=0.2, the flow enters the fan in an axial direction and is discharged radially outward at its tip, which is much like the flow characteristics of a centrifugal fan. The centrifugal effect at low flow rates makes a significant difference in performance characteristics of the fan. As the inlet flow rate increases, flow around the fan changes into the mixed type at $\Phi$=0.24 and the axial discharge at $\Phi$=0.4.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.39-45
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• 2002

Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A biaxial loading device for a single specimen is used for obtaining a wide range of mode-mixities. The specimen is an edge-cracked bimaterial strip of glass and epoxy; the biaxial loading device, being capable of controlling displacements in two perpendicular directions, is developed. A series of interfacial crack initiation and Propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. The behavior of interfacial crack propagation analyzed as a function of mode-mix shows that initial crack propagation is delayed with increase of mode-mixity, and its velocity is increased with positive mode-mixity but decreased with negative case. However, it is found that crack propagation is less accelerated with positive mode-mixity than the negative mode-mixity, which may be caused by contact and/or effects of friction between far field and near-tip Held along the interfacial crack.