• Journal of KSNVE
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• v.8 no.6
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• pp.1015-1022
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• 1998

This paper addresses the results of an experimental and analytical research of a helical coil spring subjected to dynamic behavior using space curve vector after considering elongation rate. Vibrations in helical coil spring can be divided into 3 modes such as vibrations of coil spring center axis' vertical direction. axis' horizontal direction, direction about center axis. However. these 3 modes are dependent one another and are characterized as coupled. The dependency was proved through both theoretically and experimentally analyzing the results of dynamic characteristics of coil spring center axis' vertical direction vibration by transfer matrix method using the governing equation of static equilibrium. Also this paper shows that pitch angle and active coils in coil spring affect the dynamic spring characteristics of the above 3 modes and are especially sensitive to the mode for vibration of axis' horizontal direction which most affects especially on dynamo stability of helical coil spring.

• Carbon letters
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• v.2 no.3_4
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• pp.192-201
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• 2001

The Carbon/Carbon composite was prepared from 3D carbon fiber preform and coal tar pitch as matrix precursor. In order to evaluate of ablative characteristics of the composite, liquid rocket system was employed Kerosene and liquid oxygen was used as propellants, operating at a nominal chamber pressure of 330 psi and a nominal mixture ratio (O/F) of 2.0. The results of an experimental evaluation were that high density composite exhibited high, while low density composites showed low erosion resistance. The erosion rate against heat flux was highly depended on the density of the materials. The morphology of eroded fiber showed differently according to collision angle with heat flux on the composite. The granular matrix which derived from carbonization pressure of 900 bar was more resistance to heat flux than well-developed flow type matrix.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.3
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• pp.300-306
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• 2006

In this paper an error analysis of 3-dimensional GNSS attitude determination system is given. The attitude error covariance matrix is derived and analyzed. It implies that attitude errors are affected by the baseline length and configuration, the satellites numbers and geometry, receiver measurement noises and the nominal attitude of the vehicle. By defining Euler Angle Dilution Of Precision (EADOP) which is analogous to GDOP, roll, pitch and yaw errors can be efficiently analyzed. However the expression of the attitude error is too complex to get some intuitions. Therefore with a commonly adopted assumption, new expressions for attitude error are derived. The formulas are easy to compute and represent the attitude error as a function of the nominal attitude of a vehicle, the baseline configuration and the receiver noise. Using the formula, the accuracy of the attitude can be analytically predicted without the computer simulations. Applications to some widely used configurations reveal the effectiveness of the proposed method.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.400-403
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• 2007

소형 풍력터빈 설계 시 고려해야 할 익형의 선택, 익형의 붙임각 및 Solidity 등이 터빈의 성능에 미치는 영향을 고찰하였다. 한 개의 익형에 대한 공력계수를 이용하여 수학적 모델링을 통하여 최적 붙임각을 예측하여 경향을 파악하였다. 받음각에 따른 익형의 공력특성을 CFD 기법으로 파악한 후 5개의 Blade를 갖는 Turbine의 성능을 익형의 붙임각에 따라 파악하여 최대 성능을 갖는 붙임각을 최종 산출하였다. 익형 선정시 받음각에 대한 양력/항력 곡선을 이동시키는 캠버 익형의 기능보다는 항력 대양력의 비(L/D) 가 최대인 익형을 선정하는 것이 더욱 중요하며, Blade수가 적을수록 Torque의 양은 증가하고 Blade가 6이상이변 효율이 급격히 감소함을 알 수 있다.

• Journal of the korean Society of Automotive Engineers
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• v.3 no.2
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• pp.27-33
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• 1981

In the paper, it was attempted to verify how the strength around fillet area of shifted gear would be affected by variables such as number of teeth, shifted value, and diametral pitch. Thereafter, the Lewis' tooth factor of the shifted gear was computed in terms of previously mentioned variables in order to observe the characteristics of stress change related from tooth factor and tooth number with the parameter of shifted values and diametral pitches. From the results of quasi-theoretical values by Finite Element Method(F.E.M.)and experimental values through the photo-elastic tests, the followings were identified. The more the number of gear teeth increased, the more the profile of the tooth became close to that of rack, and accordingly the stresses in the fillet area decreased significantly in certain range. Furthermore, as the shifted value and pressure angle increase the stresses tend decrease. Moreover, the stresses analyzed by F.E.M. in the filled area became around 1.22 times larger than the stresses computed by Lewis' form factor, and this is supposed as on influence of the stress concentration in fillet area.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.189-197
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• 1996

In this study, the crashworthiness analysis was carried out for the hat type section side rails which had an important role of absorbing the impact energy during frontal crash. In case of a tapered hat type section model, numerical simulation models and test models were designed with varing design variables; welding pitch, taper angle, initiator shape, initiator location. The effect of variation of the design variables was investigated by quasi-static and dynamic test and numerical simulation.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.676-685
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• 1993

A mathematical model was developed to quantify the separation process of threshed grain-straw mixtures. It was made to predict the separation loss from a separation unit consisted of stationary crimped sieve with rotating inner rotor. Experiments were performed to prove the mathematical model by changing various levels of pertinent variables for rice. Good Agreement between the simulated results and observed data under the various test conditions, such as inclination angle of the separator, vane pitch, rotor speed, MOG/G ratio, feed rate, and crop variety and moisture content, were confirmed.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.10
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• pp.497-504
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• 2005

For maximum output power, wind turbines are usually controlled at the speed which is determined by the optimal tip-speed ratio. This method requires information of wind speed and the power conversion coefficient which is varied by the pitch angle control. In this paper, a new maximum output power control algorithm using fuzzy logic control is proposed, which doesn't need this information. Instead, fuzzy controllers use information of the generator speed and the output power. By fuzzy rules, the fuzzy controller produces a new generator reference speed which gives the maximum output power of the generator for variable wind speeds. The proposed algorithm has been implemented for the 3[kW] cage-type induction generator system at laboratory, of which results verified the effectiveness of the algorithm.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1624-1627
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• 2005

We proposed a design technique for auto-landing guidance and control system. This technique utilizes linear controller and neural network. Main features of this technique is to use conventional linear controller and compensate for the error coming from the model uncertainties and/or reference model mismatch. In this study, the multi-perceptron neural network with single hidden layer is adopted to compensate for the errors. Glide-slope capture logic for auto-landing guidance and control system is designed in this technique. From the simulation results, it is observed that the responses of velocity and pitch angle to commands are fairly good, which are directly related to control inputs of throttle and elevator, respectively.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1978-1982
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• 2005

In this paper, a linear controller is designed for the longitudinal model of X-33 in TAEM (The Terminal Area Energy Management) phase. The CRA (Characteristic Ratio Assignment) is used as the continuous time design method such that the output response of X-33 control system tracks the reference command. The performance of the proposed controller is evaluated through the step response. Also simulation results show that the initial state of the plant is dominantly affected by the poles and zeros of the plant.