• 한국진공학회지
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• 제17권2호
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• pp.170-174
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• 2008

고립된 탄소나노튜브를 얻기 위해 계면활성제 Sodium Dodecyl Sulfate(SDS) 수용액에 단층 탄소나노튜브 분말을 넣어 초음파 처리를 하는 과정 중에 발생하는 물성 변화를 라만과 Photoluminescence를 통하여 연구하였다. 단층 탄소나노튜브(SWCNT) radial breathing mode(RBM)의 라만신호 세기의 변화는 SWCNT의 chirality에 따라 서로 다른 경향성을 보이고 초음파 처리 시간에 영향을 받음을 확인하였다. 또한 동일한 농도의 계면활성제에 담긴 SWCNT의 농도가 커지면 G-band 라만 진동수가 작아지면서 Photoluminescence 세기가 증가하는 현상을 관측하였다.

• Tribology and Lubricants
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• 제34권1호
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• pp.9-15
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• 2018

Modern high-performance automotive turbochargers (TCs) implement ceramic hybrid angular contact ball bearings in series with squeeze film dampers (SFDs) to enhance transient responses, thereby reducing the overall emission levels. The current study predicts the rotordynamic responses of the commercial automotive TCs (compressor wheel diameter = ~53 mm, turbine wheel diameter = ~43 mm, and shaft diameter at the bearing locations = ~7 mm) supported on ball bearings and SFDs for various design parameters of SFDs, including radial clearance, axial length, lubricant viscosity, and rotor imbalance conditions (i.e., amplitudes and phase angles) while increasing rotor speed up to 150 krpm. This study validates the predictive rotor finite element model against measurements of mass, polar and transverse moments of inertia, and free-free mode natural frequencies and mode shapes. A nonlinear rotordynamic model integrates nonlinear force coefficients of SFDs to calculate the transient responses of the TC rotor-bearing system. The predicted results show that SFD radial clearances, as well as phase angles of rotor imbalances, have the paramount effect on the dynamic responses of TC shaft motions.

• 한국소음진동공학회논문집
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• 제19권1호
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• pp.76-84
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• 2009

The vibration and stability of thin, flexible corotating disks in an enclosed compressible fluid is investigated analytically and compared with the results of a single rotating disk. The discretized dynamical system of the corotating disks is derived in the compact form of a classical gyroscopic system similar with a single disk. For the undamped system, coupled structure-acoustic traveling waves destabilize through mode coalescence leading to flutter instability. However, it is found that the flutter regions of the corotating disks are wider than those of a single disk. A detailed investigation of the effects of dissipation arising from acoustic or disk damping is also performed. Finally, in the presence of both acoustic and disk dampings, the instability regions are found and compared with those of a single disk. Although this study does not allow a radial clearance between the disk and the enclosure, the computational frame work of the problem can be expanded to the system having the radial clearance in an enclosure.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.1115-1121
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• 2017

초기 추력을 증가시키기 위하여 넓은 초기 연소 면적을 가지는 고체 로켓 모타를 설계하고 지상연소 시험을 수행하였다. 그 결과 연소 거리에 따른 연소 면적 변화를 고려한 내탄도 성능 예측에 비하여 초기 압력과 추력이 낮게 측정되었다. 연소실 내부 유속과 연소 거리에 따른 연소 속도 변화를 검토한 결과 압력에 의하여 결정되는 연소 속도 대비 연소 속도가 감소하는 negative erosive burning이 발생함을 확인하였다. 또한 8개의 대칭형 fin 형상을 적용하여 radial mode의 연소 불안정이 발생함을 확인하였으며 fin의 배치를 변경하여 대칭성을 제거함에 따라 연소 불안정이 억제되었음을 확인하였다.

• 한국군사과학기술학회지
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• 제11권5호
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• pp.92-98
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• 2008

Chaff is one of important devices for heliborne protection from radars and missiles. When we use a chaff for heliborne protection, J/S(jamming signal of chaff vs reflected signal from heliborne) is important factor to analyze a heliborne survive. When the radial angle between missile and heliborne is changed, J/S of missile receiver is changed and jamming effectiveness of chaff is also changed. We calculate the RCS of chaff and heliborne, and compare the returned signals in a half power beam width of receiver antenna. We analyze chaff dispense modes and specially simulate the effectiveness of a dilution mode chaff between missile and heliborne.

• 한국소음진동공학회논문집
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• 제12권9호
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• pp.685-693
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• 2002

Analytical model of beat response is derived on a slightly asymmetric ring and the model is veryfied by experiment. The asymmetric ring is a simplified model used to explain the beat property of a Korean bell. The asymmetric ring has mode pairs having slight frequency difference in each radial mode. Each mode pair produces beat phenomenon by the interaction of the two close frequency components. Based on the analytical model, beat maps are first proposed and characteristics of beat on the circumference are detaily explained.

• 대한전기학회논문지:시스템및제어부문D
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• 제49권5호
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• pp.269-277
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• 2000

We propose two new types multi-stage blind clustering equalizers for QAM demoulation, which are called a complex classification algorithm(CCA) and a radial basis function algorithm(RBFA). The CCA uses a clustering technique based on the joint gaussian probability function and computes separately the real part and imaginary part for simple implementation as well as less computation. In order to improve the performance of CCA, the Dual-Mode CCA(DMCCA) incorporates the CCA tap-updating mode with the decision-directed(DD) mode. The RBFA reduces the number of cluster centers through three steps using the classification technique of RBF and then updates the equalizer taps for QAM demodulation. Test results on 16-QAM confirm that the proposed algorithms perform better the conventional multi-state equalizers in the senses of SER and MSE under multi-path fading channel.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1716-1721
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• 2006

The Lubrication Mode of line contacts between the vane and the camring in an oil hydraulic vane pump has been investigated. First, the variations of the radial force of a vane were calculated from previous measurements of dynamic internal pressure in four chambers surrounding a vane. Next, the lubrication modes were distinguished with Hooke's chart, which is an improvement over Johnson's chart. Finally, the influence of the boundary conditions in the lubrication region on the fluid film lubrication was examined by calculating the film pressure distributions. The results showed that the lubrication mode of the vane tip exists in the rigid-variable-viscosity region, and that discharge pressure higher than 7 MPa greatly affects the oil film pressure in the small and the large arc section because of the Piezo-viscous effect.

• Computers and Concrete
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• 제14권6호
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• pp.675-694
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• 2014

Annular and solid concrete specimens with different aspect ratios and static unconfined compressive strengths were studied for impact loading using SHPB test setup. Numerical simulations in LSDYNA were also carried out and results were validated. The stress-strain curves obtained under dynamic loading were also compared with static compressive tests. The mode of failure of concrete specimen was a typical ductile failure at high strain rates. In general, the dynamic increase factor (DIF) of thin solid specimens was higher than thick samples. In the numerical study, the variation of axial, hydrostatic and radial stresses for solid and annular samples was studied. The core phenomenon due to confinement was observed for solid samples wherein the applied loads were primarily borne by the innermost concrete zone rather than the outer peripheral zone. In the annular samples, especially with large diameter inside hole, the distribution of stresses was relatively uniform along the radial distance. Qualitatively, only a small change in the distribution of stresses for annular samples with different internal diameters studied was observed.

• 한국추진공학회지
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• 제12권2호
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• pp.1-7
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• 2008

연소실내 음향 감쇠를 위해 장착되는 반파장 공명기의 반경 방향 위치 효과를, 상온에서의 선형 음향 실험을 통해 실험적으로 연구하였다. 음향 감쇠의 정량화를 위해 감쇠 인자를 사용하였다. 감쇠하고 하는 음향 모드에 대해 공명기가 최적의 길이를 갖는 경우에는, 반경 방향 위치의 증가에 따라 음향 감쇠 효과가 증가하였다. 또한, 감쇠 인자의 변화 추이는 감쇠시키고자 하는 음향 모드의 진폭 변화 추이와 유사하였다. 장착 위치가 장착면의 중심에 접근할수록 음향 감쇠 효과가 감소할 뿐만 아니라 분사기 길이와의 상관성토 감소하였다. 한편, 공명기가 비최적 길이를 갖는 경우에는, 반경 방향 위치 효과가 거의 나타나지 않아 위치와 무관한 감쇠 인자값을 관찰할 수 있었다. 공명기의 길이와 위치에 따라 감쇠 성능을 평가하였다.