• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.181-185
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• 2010

고체로켓모터 추진제 그레인의 핀-슬롯 표면에서의 연소로 인해 생성된 고온, 고압의 연소가스는 그레인 핀-슬롯 및 내삽노즐을 통해 외부로 방출되면서 형성되는 유동은 매우 복잡하고 다양한 형태를 가진다. 핀-슬롯형 그레인 및 내삽노즐을 가지는 고체로켓모터의 2D, 3D 스케일모델에 대한 공기유동 모사시험을 수행하였으며, 회전력 발생 등과 같은 내부유동발생 메커니즘을 규명할 수 있는 효과적인 연기-유동장 가시화 기법의 적용방법에 대한 검토가 이루어 졌다. 실험모델의 투영부를 통해 다양한 광원 및 촬영장치 방향을 이용하여, 축류 실험모델 노즐 선단부에서의 비대칭 와류튜브에 의한 선회류를 가시화하였다.

• 한국자동차공학회논문집
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• 제14권6호
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• pp.184-189
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• 2006

Tumble flow test rig has been used as the useful tool in the developing intake system because major flow pattern induced by intake port of DOHC engine is tumble. Angular momentum of in-cylinder tumble flow can not be directly measured by impulse torque meter in the test rig like that of in-cylinder swirl flow due to rotational axis of the flow. Therefore the adaptor to transform tumble to swirl flow must be adapted in the test rig. In this study, using the commercial CFD code STAR-CD, we studied the effects on measured results due to the variation of the major design variables in the adaptor, tube length(L), tube diameter(D) and cylinder height(H). The effect of the attached angle($\theta$) of the test head to the adaptor also was simulated.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.375-382
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• 2009

Hydraulic instability associated with pressure fluctuations is a serious problem in hydraulic machinery. Pressure fluctuations are usually a result of a strong vortex created in the centre of a flow at the outlet of a runner. At every radial turbine and also at every single regulating axial turbine, the draft tube vortex appears at part-load operating regimes. The consequences of the vortex developed in the draft tube are very unpleasant pressure pulsation, axial and radial forces and torque fluctuation as well as turbine structure vibration. The consequences of the vortex are transferred upstream and downstream with amplitude and frequency modulation in respect of the turbine operating regime, cavitation conditions and air admitted content. Numerical prediction of the vortex appearance in the design stage is a very important task. The amplitude of the pressure pulsation is different for each operating regime therefore the main goal of this research was to numerically predict pressure pulsation amplitude versus different guide vane openings and to compare the results with experimental ones. For the numerical flow analysis of a complete Francis turbine (FT), the computer code ANSYS-CFX11 has been used.

• Composites Research
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• 제19권3호
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• pp.29-36
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• 2006

섬유강화 복합재료는 적층각도와 적층순서에 따라 이방성을 가지기 때문에, 복합재료가 튜브형 접합부의 피접착체로 사용될 경우 지금까지 많이 수행된 등방성 피접착체를 가지는 접합부에 대한 해석을 통하여 복합재료 접합부의 거동을 예측하는 것은 한계가 있다. 본 연구에서는 접착제의 비선형 거동을 고려하여 복합재료 피접착체를 가지는 튜브형 접합부에 대한 비선형 해석을 수행하였다. 먼저 적층 복합재료 튜브에 대한 해석을 수행하였고, 이를 바탕으로 튜브형 접합부에 대한 비선형 방정식을 유도하였으며, 접착층의 응력 분포 및 접합부의 토크전달능력을 계산하였다. 복합재료 튜브의 적층순서와 접착길이가 접착층의 응력 분포 및 토크전달능력에 어떤 영향을 미치는 지 살펴보았으며, 또한 비선형 해석과 선형해석의 차이점을 비교하고 분석하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.226-231
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• 2004

Press fitting method for joining of a hybrid tube and steel ring with small teeth for automotive aluminum/composite hybrid propeller shaft was devised to improve reliability and to reduce manufacturing cost, compared to other joining methods such as an adhesively bonded joint, bolted joint or welded joint. To obtain high strength of the press fit joint, an optimal design method for the teeth was devised with respect to number and shape of the steel teeth. Torsional static, fatigue tests and finite element analysis of the press fit joint were performed with respect to experimental variables. The developed optimal design method predicted well the static torque capability and failure mode of the press fit joint. Also, it provided design guide line of press fit joint for improving torsional static and fatigue characteristics.

• 한국자동차공학회논문집
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• 제1권3호
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• pp.109-117
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• 1993

A carbon/epoxy composite drive shaft used for the power transmission of the automobiles with steel joints. Compared with the metallic drive shaft, the composite one has the weight saving of 50% with equivalent torsional strength and fatigue characteristics. In this study, the filament winding technique for the composite tube and composite/metal joining technique are estabilished. The performance test of the drive shaft is carried out. The optimal condition of the surface roughness of the steel adherend was $1.5{{\mu}m}$ to $2.5{{\mu}m}$, and the optimal condition of the bonding thickness was 0.15mm. Maximum torque and torsional stiffness of the composite drive shaft manufactured by filament winding process were found to be $210kg{\cdot}m$ and $18.5kg{\cdot}m/deg$, respectively.

• 설비공학논문집
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• 제9권4호
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• pp.446-453
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• 1997

The superconducting winding in rotor of a superconducting generator should be kept at extremely low temperature of 4-5 K to maintain the superconducting state. For this purpose the liquefied helium is used for the coolant and it is very important to analyze and design a cooling system making effective use of the coolant. In this paper, the typical heat exchanger of a superconducting generator with the flow passage is analyzed with regard to the thermal equilibrium. An experimental constant relevant to the flow condition in the flow passage is determined with heat exchange experiments in cryostat. Also a new heat exchanger with porous material is proposed and designed. Results of the numerical analysis for the temperature distributions for the torque tube and the coolant are reported and the efficiency of the heat exchanger is discussed from the viewpoint of amounts of coolant needed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.103-108
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• 2013

This paper describes basic properties tests and non-rotating dynamic test for rotor blade, flexbeam, and torque tube of which bearingless rotor in helicopter consists. A basic properties test are bending and twist test to find the flap stiffness, lag stiffness, and twist stiffness of specimens. The purpose of dynamic test is to find natural frequencies and modes in non-rotating state. The test results are used to update the analysis model. The updated analysis results using rotorcraft comprehensive code match the tests quite well. The updated model input based on the tests will be utilized to analysis the conditions of rotating whirl tower test before the whirl test and will be compared with the whirl tower test results.

• 한국정밀공학회지
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• 제15권10호
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• pp.65-72
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• 1998

The BTA drilling chip is better for deep hole drilling than other self-piloting with pad drilling chips because the large length to diameter ratio allows a unique cutting force dispersion and better supplies the high pressure fluid. Therefore the BTA is useful for many tasks, such as coolant hole drilling of large scale dies, as well as tube seat drilling, which is essential for the heat exchanger, and variable component drilling for automobiles. Deep hole drilling has several significant problems, such as hole deviation, hole over-size, circularity, straightness, and surface roughness. The reasons for these problems, which often result in quality short comings, are an alignment of the BTA drilling system and the unbalance of cutting force by work piece and tool shape. This paper analyzes the properties through an experiment which com¬pared single-edge BTA drills with multiple-edge BTA drills, as well as the shapes of the tools to cause an unbalance of cutting force, and its effect on the precision of the worked hole. Conclusions are as follows. 1) In SMSSC drilling, 60m/min of BTA with single and multi-edged tools proved the best cutting condition and the lowest wear character. 2) The roundness got a little worse as cutting speed was increased, but surface roughness was hot affected. 3) It was proved that the burnishing torque of both drills approached 26%. which is almost the same as the 24% insisted on by Griffiths, and the dispersion characteristic of the multi-edged BTA drill proved better than the single-edge BTA drill.

• 천문학회지
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• 제36권1호
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• pp.33-41
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• 2003

Recent observations have shown that coronal magnetic fields in the northern (southern) hemisphere tend to have negative (positive) magnetic helicity. There has been controversy as to whether this hemispheric pattern is of surface or sub-surface origin. A number of studies have focused on clarifying the effect of the surface differential rotation on the change of magnetic helicity in the corona. Meanwhile, recent observational studies reported the existence of transient shear flows in active regions that can feed magnetic helicity to the corona at a much higher rate than the differential rotation does. Here we propose that such transient shear flows may be driven by the torque produced by either the axial or radial expansion of the coronal segment of a twisted flux tube that is rooted deeply below the surface. We have derived a simple relation between the coronal expansion parameter and the amount of helicity transferred via shear flows. To demonstrate our proposition, we have inspected Yohkoh soft X-ray images of NOAA 8668 in which strong shear flows were observed. As a result, we found that the expansion of magnetic fields really took place in the corona while transient shear flows were observed in the photosphere, and the amount of magnetic helicity change due to the transient shear flows is quantitatively consistent with the observed expansion of coronal magnetic fields. The transient shear flows hence may be understood as an observable manifestation of the pumping of magnetic helicity out of the interior portions of the field lines driven by the expansion of coronal parts as was originally proposed by Parker (1974).