• 한국자동차공학회논문집
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• 제24권6호
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• pp.642-648
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• 2016

This paper deals with an analytical and experimental investigation to predict the axial thrust load that results from turbocharger operating conditions. The Axial forces acting on the turbocharger thrust bearing are caused by the unbalance between turbine wheel gas forces and compressor wheel air forces. It has a great influence on the friction losses, which reduces the efficiency and performance of high-speed turbocharger. This paper presents the calculation procedure for the axial thrust forces under operating conditions in a turbocharger. The first step is to determine the relationship between thrust forces and strains by experimental and numerical methods. The analysis results were verified by measuring the strains on a thrust bearing with the specially designed test device. And then, the operating strains and temperatures were measured to inversely calculate the thrust strains which were compensated the thermal effects. Therefore it's possible to calculate the magnitudes of the thrust forces under operating turbocharger by comparing the regenerated strains with the rig test results. It will possible to optimize the design of a thrust bearing for reducing the mechanical friction losses using the results.

• 한국항공운항학회지
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• 제29권1호
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• pp.61-73
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• 2021

PAV is considered to improve quality of life and standards of living, improvement of which was caused by automobile hundred years ago. Comparative economic efficiency of PAVs is measured to compare each PAV. Specification and sales price of the PAVs are open to the public. BlackFly, Transition and Aeromobil 3.0 have competitive power in flying range, purchasing cost, and operational cost. Lift & cruise configuration and vectored thrust configuration PAVs are designed by many companies nowadays, and BlackFly which can be considered to be lift & cruise configuration is one of the most efficient PAVs. High battery price does not help multi-copter shaped PAVs to have economic efficiency. Aerodynamic wing, eVTOL, and low sale price are needed for PAVs to ride a wave of public interest as a new personal mobility. Under the conditions, the PAV can fly at downtown and can be purchased by people at large. Popularization of PAV could follow in the 100 years old footsteps of automobile.

• 제어로봇시스템학회논문지
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• 제18권2호
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• pp.103-109
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• 2012

Fish generates large thrust through an oscillating motion with a compliant joint of caudal fin. The compliance of caudal fin affects the thrust generated by the fish. Due to the flexibility of the fish, the fish can generate a travelling wave motion which is known to increase the efficiency of the fish. However, a detailed research on the relationship between the flexible joint and the thrust generation is needed. In this paper, the compliant joint of a caudal fin is implemented in the driving mechanism of a robotic fish. By varying the driving frequency and stiffness of the compliant joint, the relationship between the thrust generation and the stiffness of the flexible joint is investigated. In general, as the frequency increases, the thrust increases. When higher driving frequency is applied, higher stiffness of the flexible joint is needed to maximize the thrust. The bending angles between the compliant joint and the caudal fin are compared with the changes of the thrust in one cycle. This result can be used to design the robotic fish which can be operated at the maximum thrust condition using the appropriate stiffness of the compliant joint.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.473-477
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• 2005

This paper presents a highly efficient HDD (Hard Disk Drive) spindle motor with a passive magnetic thrust bearing and a fluid dynamic journal bearing and its effectiveness is verified through experiment. It eliminates the mechanical friction loss of a thrust bearing which is around 18% of total power consumption of a 3.5' HDD spindle motor, by replacing a conventional fluid dynamic thrust bearing with a passive magnetic thrust bearing. The passive magnetic thrust bearing using permanent magnets is inherently unstable in radial direction. However, the radial fluid dynamic force of the fluid dynamic journal bearing counterbalances the radial magnetic force of magnetic thrust bearing to achieve the stability as the motor spins up. It has less or equivalent runout and less flying height than the conventional spindle motor.

• 한국항공우주학회지
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• 제34권1호
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• pp.32-41
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• 2006

본 논문에서는 직렬 배치된 익형이 동시에 플래핑 운동을 할 때의 추력 생성 과정과 유동특성에 대한 연구를 수행하였다. 이를 위해 익형의 운동 주파수, 진폭 및 전후방 익형 간의 상대거리 등에 대한 계산을 체계적으로 실시하여 다음과 같은 사실을 확인할 수 있었다. 먼저, 위상차 없이 전후방 익형이 동시에 병진운동을 할 경우 대부분의 주파수와 진폭 영역에서 후방익형의 추력과 추진효율이 최대화됨을 알 수 있었다. 플래핑 진폭이 0.2 코드, 무차원주파수가 0.75일 경우, 후방익형의 추진효율이 전방익형보다 37% 이상 개선되는 것으로 계산되었다. 단, 익형의 운동 진폭과 주파수가 임계치를 초과할 경우 전방익형의 뒷전와류에 의해 후방익형의 앞전와류의 강도가 강화되면서 전체적인 추력과 효율이 저하될 수 있다. 둘째, 전후방익형이 180도의 위상차를 갖고 운동을 할 경우에는 전방익형의 후류와 후방익형이 서로 반대방향으로 상호작용을 함으로써 결과적으로 공력특성이 악화되는 것을 알 수 있었다. 셋째, 후방익형의 배치 위치에 따른 특성은 수평방향으로는 두 익형사이의 거리가 멀어질수록 추력과 효율이 동시에 떨어지며, 수직방향 위치변화에 따른 차이는 크지 않은 것으로 나타났다.

• Tribology and Lubricants
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• 제25권5호
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• pp.292-297
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• 2009

Air foil thrust bearings are the critical components available on high-efficiency turbomachinery which need an ability to endure the large axial force. Air foil bearings are self-acting hydrodynamic bearings that use ambient air as their lubricant. Since the air is squeezed by the edge of compliance-surface of bearing, hydrodynamic force is generated. In this study, we measured the air film thickness and obtained the minimum film thickness experimentally. To increase the maximum load capacity, compliance of sub-structure was controlled. From numerical analyses, it is seen that, if the air film thickness is distributed more uniformly by variable compliance, the thrust bearings can take more axial load.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권1호
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• pp.27-33
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• 2005

The development of modern high-energy magnet materials has allowed the replacement of field coils in many different types of electromagnetic energy conversion machines. As well, the linear synchronous motor has recently been proposed for linear motion with high efficiency and thrust. Thus, this paper presents an analytical solution for the high thrust and cost reduction of the Iron-Cored Permanent Magnet Linear Synchronous Motor (PMLSM) considering magnetization arrays and geometry. Hence, the superior utilization points in each of the magnetization arrays are provided by the height ratio of the magnet/air-gap and magnet/winding coil, etc. In formulation, the space harmonic method in analytical solutions and the generalized 2-D tensor finite element analysis can be used to evaluate force components in magneto static devices including the magnetostrictive phenomenon.

• 한국유체기계학회 논문집
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• 제10권4호
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• pp.15-20
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• 2007

In order to control and balance axial thrust of turbo machine, many types of balancing devices are used but most of them are complicated and sometimes cause troubles. In this study, a very simple device of using shallow grooves mounted on a casing wall, known as "J-Groove", is proposed and studied experimentally and theoretically. The result shows that 70% of axial thrust in an industrial 4-stage centrifugal pump can be reduced at the best efficiency point. Moreover, the analytical method of "interfered gap flow" is established and a simple formula which can determine the optimum dimension of groove and its location is proposed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.258-262
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• 2010

Since MEMS based micro actuators or generating devices showed high efficiency per volume, plenty of research are ongoing. Among them, MEMS based millimeter-scale micro gas turbine is one of the most powerful item for replacing chemical batteries. However, due to MEMS manufacturing technique, it is very difficult that makes wide turbine bearing area. It causes low DN number, so sufficient bearing force is hard to achieve. Thus, the most important issue on micro gas turbine is to design the proper bearing which can keep rotor stable during operation. In order to that, micro-scale gas-lubricated bearing is generally used. In this paper, basic feasibility study of thrust bearing of 10mm diameter turbine is described. Thrust bearing is hydrostatic gas-lubricated type. Numerical simulation is performed with ANSYS CFX 11.0 which is commercial numerical tool. Relationship between bearing inlet pressure and mass flow rate and bearing force is figured while changing bearing gap and number of capillaries. The simulation results will be used for further design of micro gas turbine.

• 대한기계학회논문집B
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• 제21권4호
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• pp.562-569
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• 1997

The axial position of an impeller is misaligned in the process of manufacturing and assembling. For a single suction centrifugal pump with balancing holes, the effect of axial displacement of impeller on the performance, leakage loss and axial thrust acting on the impeller is experimentally investigated. The axial displacement decreases the pump efficiency, increases the leakage through the clearance between wearing ring and impeller, and affects the characteristics of axial thrust.