• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.1
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• pp.50-58
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• 1998

Water vapor transmission was tested in water bath controlled by $20^{\cire}C$, 90%RH for T800/AD6005 based composite motor case which made by filament winding method. We detected internal relative humidity of composite motor case by inserting the humidity detector through the head of motor case for the study of humidity transmission through the wall of composite motor case. We found out that this composite material appears the water vapor flux of 2.88${\times}$$10^{-9}$g/$\textrm{m}^2$sec and diffusivity of 7.98${\times}$$10^{-7}$$\textrm{mm}^2$/sec at $20^{\cire}C$, 90%RH water vapor condition.

• Composites Research
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• v.14 no.1
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• pp.39-46
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• 2001

Experimental studies on the adaptive multi-mode vibration control of composite beams have been performed using neuro-controller. Neuro-controllers require too much computational burden, which blocks wide real-time applications of neuro-controllers. Therefore, in this paper, an adaptive notch filter is proposed to separate a vibration signal into each modal vibration signal. Two neuro-controllers with fewer weights are connected to the corresponding modal signals to generate proper modal control forces. The vibration controls using the adaptive notch filter and neuro-controllers have been performed for two specimens. A and B, which have different natural frequencies because of different positions of tip masses. Significant vibration reduction has been observed in both cases. The vibration control results show that the present neuro-controller has good adaptiveness under the system parameter variations.

• Composites Research
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• v.12 no.2
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• pp.1-9
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• 1999

The piezoelectric material connected to external electric networks possesses frequency dependent stiffness and loss factor which are also affected by the shunting circuit. The external electric networks are generally specialized for two shunting circuits: one is the case of a resistor alone and the other is the combination of a resistor and an inductor. For resistive shunting, the material properties exhibit frequency dependency similar to viscoelastic materials, but are much stiffer and more independent of temperature. Shunting with a resistor and inductor introduces an electrical resonance, which can change the characteristics of structural resonance optimally in a manner analogous to a PMD (proof mass damper). Passive damping enhancement of composite beam using piezoelectric material connected to external electrical networks is achieved and presented in this paper.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.7
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• pp.561-568
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• 2013

After we designed Bearingless rotor hub system for 7,000lb class helicopter, flexbeam fatigue analysis was conducted for validation of requirement life time 8,000 hours. sectional structural analysis method applying elastic beam model was used. Fatigue analysis for two sections of flexbeam which were expected to weak to fatigue damage from result of static analysis was conducted. Extension, bending and torsion stiffness of flexbeam section shape was calculated using VABS for structure analysis. S-N curve of two composite material which composed flexbeam was generated using wohler equation. Load analysis of bearingless rotor system was conducted using CAMRAD II and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used flexbeam fatigue safe life analysis.

• Composites Research
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• v.32 no.1
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• pp.45-49
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• 2019

Fiber reinforced composites fabricated by the resin film infusion (RFI) process, which is one of the outof-autoclave process, have the advantage of significantly reducing the processing cost in large structures while having excellent mechanical properties and uniform impregnation of the resin. In this study, we applied RFI carbon fiber composites to unmanned aerial vehicle structures to improve structural safety and achieve weight reduction. The tensile test results showed that the strength was 46% higher than that of generic T300 grade plain weave carbon fiber composites. As a result of the layup design and finite element analysis of the composite wing structure using the above material properties, the wing tip deflection is decreased by 31%, the structural safety factor is increased by 28% and the weight of the entire structure can be reduced by more than 10% compared to the reference model using glass fiber composite material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.745-751
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• 2011

This study proposes finite element modeling of dislocation punching at cooling after consolidation in order to calculate the strength of particle-reinforced aluminum composites. The Taylor dislocation model combined with strain gradient plasticity around the reinforced particle is adopted to take into account the size-dependency of different volume fractions of the particle. The strain gradients were obtained from the equivalent plastic strain calculated during the cooling of the spherical unit cell, when the dislocation punching due to CTE (Coefficient of Thermal Expansion) mismatch is activated. The enhanced yield stress was observed by including the strain gradients, in an average sense, over the punched zone. The tensile strength of the SiCp/Al 356-T6 composite was predicted through the finite element analysis of an axisymmetric unit cell for various sizes and volume fractions of the particle. The predicted strengths were found to be in good agreement with the experimental data. Further, the particle-size dependency was clearly established.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.317-323
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• 2022

In this paper, a deep neural network(DNN) model for predicting the vibration characteristics of the composite rotor blade with c-spar cross section was developed. Herein, the present DNN model is defined by using the natural frequencies obtained through the in-house code based on the nonlinear co-rotational(CR) shell element. For the present DNN model, the accuracy of the model was evaluated via the data with a random distribution of thickness and a tendency to decrease in thickness along the blade span.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.42-48
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• 2009

There are a number of factors affecting the continued airworthiness of composite structure. Unlike metal structure, damages made in manufacturing processes or maintenance repair procedures need to be considered. The different levels of degradation and damage, which may occur, must be considered for structural substantiation of static strength, stiffness, flutter, and damage tolerance. This can start with an evaluation of environmental effects for the particular composite material. Matrix-dominated composite properties, such as compressive strength, are most sensitive to moisture absorption and temperatures. Static strength substantiation includes the smaller damages that will not be detected in production or maintenance inspection while damage tolerance addresses larger damages that need to be repaired once discovered. In this paper, we intend to list the airworthiness regulations and advisory circular that are deemed closely related to the certification of composite airplanes.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.478-480
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• 2002

인터넷을 기반으로 한 고품질 오디오 스트리밍 서비스를 위하여 오디오 데이터 전송 시 발생되는 품질의 열화를 극복하여 고품질의 오디오 재생이 가능한 QoS 보장기법을 제안한다. 오디오 데이터는 연속성과 시간제약성을 가지고 있기 때문에 전송 시 통신망의 상황에 따라 그 재생품질이 결정된다. 이때 필요한 QoS 보장 기법으로 통신망의 상황에 따라 동적으로 전송률을 가변시키고 ARQ에 의한 재전송 방식과 동적 버퍼 제어기법을 복합적으로 적용하는 기법을 보인다. 클라이언트 내의 오디오 데이터 버퍼를 현재 망 상황에 따라 제어함으로서 재전송에 필요한 시간을 확보하고, 전송률도 함께 연동 조정하여 재전송에 따른 전송률 저하 현상을 방지한다. 동적인 클라이언트 버퍼/전송률 제어에 필요한 파라미터는 현재 통신망에서의 UDP 패킷 에러율과 왕복시간 이다. 실제 인터넷 환경에서 위 복합적 QoS 보장기법을 적용하여 고품질로 재생되는 오디오 스트리밍 서비스의 성능을 확인하였다.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.123-126
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• 2004

Two-way shape memory effect(TWSME) under residual stresses are considered in the present study. The structure using two-way shape memory effect concept returns to its initial shape by increasing or decreasing temperature under the initially given residual stress. In the present study, we use a thermo-mechanical constitutive equation of SMA and laminated composite beam are considered as simple morphing structural components which are based on large deformable 2D composite beam theory. Numerical results of fully coupled SMA-composite structures are presented.