• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.205-211
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• 2006

Among other critical conditions in rotor systems the large non-linear vibration excited by bearing non-linearity causes the rotor failure. For reducing this catastrophic failure and predictive detection of this phenomenon the analysis of orthotropic bearing non-linearity in rotor system using higher order frequency response functions (HFRFs) is conducted and is shown to be theoretically feasible as that of non-rotating structures. The complex HFRFs based on the Volterra series are newly developed for the process and investigated their features by using the simple forms of the FRFs associated with the forward and the backward modes.

• International Journal of Aeronautical and Space Sciences
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• 제5권2호
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• pp.35-42
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• 2004

Among other critical conditions in rotor svstems the large non-linearvibration excited by bearing non-linearity causes the rotor failure. For reducing thiscatastrophic failure and predictive analysis of this phenomena the identificationanalysis of bearing non-linearity in an anisotropic rotor system using the higherorder dFRFs are developed and are shown to be theoretically feasible as innon-rotating structures. For the identification of the anisotropic rotor withanisotropic bearing non-linearity expressed by the displacement in polynomial form,the higher order dFRFs based upon the Volterra series are investigated and depicttheir features by using the simple forms of the normal and reverse dFRFs. Theyproduce additional sub-harmonic resonant peaks, which indicate the existence ofhigher order non-linearties, and show the energy transfer such that the modes fornormal and reuerse dFRFs are exchanged, which are the fundamental differencesfrom what we can expect in linear ones.

• KSTLE International Journal
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• 제1권2호
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• pp.107-112
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• 2000

In case of the limitation of Deep RIE fabrication far Micro Gas Turbine, bearing aspect ratio is limited in very small value. The characteristics such as pressure distribution, load capacity and non-linearity of a short bearing of L/D=0.083 and a conventional bearing of L/D=1.0 with coupled boundary effects are investigated for Micro Gas Turbine bearings. The coupled effect was analyzed by mass conservation at coupled end area. The results, increasing load capacity and non-linearity due to the coupled effect of thrust and journal bearing, are obtained and the selection of journal bearing type is discussed.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.243-249
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• 2000

In case of the limitation of Deep RIE fabrication for Micro Gas Turbine, bearing aspect ratio is limited in very small value. The characteristics such as pressure distribution load capacity and non-linearity of a short bearing of L/D=0.083 and a conventional bearing of L/D=1.0 with coupled boundary effects are investigated far Micro Gas Tlubine bearings. The coupled efffect was analyzed by mass conservation at coupled end area. The results, increasing load capacity and non-linearity due to the coupled effect of thrust and journal bearing, are obtained and the selection of journal bearing type is discussed.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.87-90
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• 2004

In this paper, geometrically non-linear finite element analyses were performed to study the mechanical behavior of the material system of the envelope of stratospheric airships. The microstructure of the load­bearing plain weave layer was identified and modeled. The Updated Lagrangian formulation was employed to consider the geometric non-linearity as well as the induced structural non-linearity for the fiber tows. The stress-strain behavior was predicted and the effective elastic modulus was calculated by numerical experiments. It was found the non-linear stress-strain curves were largely different from those by linear analysis with much higher non-linear elastic moduli. The difference was more distinguishable when the tow waviness was smaller.

• 한국정밀공학회지
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• 제22권8호
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• pp.50-56
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• 2005

This paper is described a development of an optical fiber displacement sensor. The optical fiber sensor using an intensity modulated measures the displacement between target and sensor. A prototype sensor is composed of a transmitting part, a receiving part and a signal processing circuit. The experiment was conducted not only the sensor performance but also factors that affect intensity. The main performance of this sensor is resolution of 0.37um and the non-linearity $0.7\%$ FS and the dynamic bandwidth of about 6.3kHz. As a result of rotation test, the prototype sensor showed an equivalent performance to a commercial eddy current sensor.

• Composites Research
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• 제18권2호
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• pp.30-37
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• 2005

본 논문에서는 평직구조를 갖는 성층권 비행선 기낭의 하중막재에 대한 비선형 유한요소 해석 결과를 기술하였다. 평직구조를 갖는 하중막재의 미세구조를 3차원적으로 구현하였고, Updated Lagrangian 방법을 사용하여 기하학적 비선형성을 고려하였다 계산결과, 큰 변형률에서 비선형해석으로부터 얻은 응력-변형률 곡선은 선형해석의 결과와 큰 차이를 보였다. 또한 응력-변형률 곡선으로부터 얻은 비선형 탄성계수 값은 선형 탄성계수보다 큰 값을 보였는데 그 차이는 섬유의 굴곡도가 작은 경우 더욱 두드러지게 나타났다

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.3-6
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• 2000

The magnetic bearing system are intrinsically unstable, and need the feedback control of electromagnetic forces with measured displacements. So the controller design plays an important role in constructing high performance magnetic bearing system. In case of magnetic bearing system, the order of identified model is high because of unknown dynamics included in closed loop systems - such as sensor dynamics, actuator dynamics - and non-linearity of magnetic bearings itself. In this paper the identification and robust control of flexible rotor supported by magnetic bearing are discussed. We measure and identify overall system that contains not only flexible rotor model but also magnetic bearing and time delay. The structured and unstructured uncertainties are modeled that cover variations of natural frequencies, uncertainties in sensor and actuator gains and unmodeled dynamics. And desired performances are specified with several weighting function. Using augmented system that includes identified model, uncertainties, and weighting functions, μ-synthesis is applied to flexible rotor supported with magnetic bearing. The flexible rotor was spin up over the first flexible critical speed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.493-498
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• 2000

The magnetic bearing systems are intrinsically unstable, and need the feedback control of electromagnetic forces with measured displacements. So the controller design plays an important role in constructing high performance magnetic bearing system. In case of magnetic bearing systems, the order of identified model is high because of unknown dynamics included in closed loop systems - such as sensor dynamics, actuator dynamics-and non-linearity of magnetic bearings itself. "Identification for control" - joint optimization of system identification and controller design- is proposed to get the limited-order model which is suited for the design of high-performance controller. We applied the joint identification/controller design scheme to MIMO rigid rotor system supported by magnetic bearings. Firs, we designed controller of a nonlinear simulation model of MIMO magnetic bearing system with this scheme and proved its feasibility. Then, we performed experiments on MIMO rigid rotor system supported by magnetic bearings, and the performance of closed-loop system is improved gradually during the iteration.

• 대한의용생체공학회:의공학회지
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• 제28권2호
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• pp.310-315
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• 2007

The axial-flow type blood pump(XVAD) which has been developed in our group consists of mechanical parts (an impeller, a diffuser and a flow straightener) and electrical parts (a motor and a magnetic bearing). The magnetic bearing system fully levitates the impeller to remove mechanical coupling with other parts of the pump with constant gap, which needs non-contact type gap sensing. Conventional gap sensors are too large to be adopted to the implantable axial -flow type blood pump. Thus, in this paper, the compact eddy current type gap sensor system proper for the implantable axial-flow type blood pump was developed and its performance was evaluated in vitro. The developed eddy current type gap sensor system is a transformer type and has a differential probe. Sensor coil(probe) has small dimensions(6 mm diameter, 2 mm thickness) and its optimal inductance was determined as 0.068 mH for the measurement range of $0\sim3mm$. It could be manufactured with 130 turns of the 0.04 mm diameter copper coil. The characteristics of the developed eddy current type gap sensor system was evaluated by in vitro experiment. At experiment, it showed satis(actory performance to apply to the magnetic bearing system of the XVAD. It could measure the gap up to 3mm, but the linearity was decreased at the range of $1.8\sim3.0mm$. Moreover, it showed no difference in different media such as the water and the blood at the temperature range of $35\sim40^{\circ}C$.