• 대한조선학회지
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• 제1권1호
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• pp.9-16
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• 1964

As a pre-study for researches on powering characteristics of straight-framed V-bottom hull forms for usual commercial vessels, practicability of such a hull is investigated from viewpoints of over-all ship economy. For this purpose, a trawler hull of straight-elements with double chines, SV(T)-1, similar to Prof. Nevitt's W-8 in size and hull form coefficients was designed and tested at the SNU Ship Model Towing Tank for resistance measurements. The result is given in Fig.3 together with those of W-8 and other equivalent hulls of double curvature, such as FAO 135a-173, Doust and Takgi. The curves of the latters are reproduction of Prof. Nevitt's analysis, and given for comparison purpose. With in speed range of $9.0{\sim}10.5$ konts the resistance coefficients of SV(T)-1 are $18{\sim}25%$ higher than those of W-8, and $5{\sim}20%$ and $12{\sim}14%$ higher than those of FAO 135a-173 and Doust respectively. SV(T)-1, however, is slightly superior in resistance characteristics than Takagi's equivalent hull within the speed range. On the other hand, an equation for reduction rates of hull construction cost required to compensate for propulsion power increase in straight-elements hulls was derived from the definition of the economic efficiency of commercial vessels. The solution of the equation is given in Fig.4 graphically, from which it is known that $10{\sim}20%$ increase in propulsion power can be compensated by $8{\sim}16%$ reduction in hull construction cost. Considering simplicity and less equipments required in construction of straight -elements hulls, the author does argue for attainability of the above reduction rates in hull construction cost. Consequently, it is concluded that there is clear feasibility to adopt straight-elements hulls for usual commercial vessels of medium and small-size. And a further research will be done to obtain reliable data for chine shapes having good flowliness with the flow around ships depending on ship's size and speed.

• 한국전산구조공학회논문집
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• 제30권5호
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• pp.427-434
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• 2017

최근 테러에 대한 위험성의 증가로 대중들의 폭발 피해에 대한 인식이 증가하였다. 우리나라에 방폭 설계에 대한 기준이 미흡하며, 현재 적용하고 있는 방폭 설계도 정적해석으로 건물의 안정성 및 경제성을 위해 방폭 설계를 개발해야 하는 상황이다. 또한 지진 발생 증가로 내진 설계 의무화가 확대된 가운데 방폭 설계를 하지 않고 내진 설계를 적용한 부재의 방폭성능을 판단을 연구한다. 현재 보편적인 폭발 하중의 해석 방법은 UFC 3-340-02 매뉴얼을 참고하는 것이다. UFC 3-340-02 매뉴얼을 통한 폭발 하중의 특성을 적용하고 KBC 2016의 내진 상세를 적용한 보를 등가 단자유도 시스템으로 변환하여 폭발저항 성능을 연구하였다. 보통, 중간, 특수 모멘트 골조의 연성 능력에 대한 최대 처짐을 고려하여 폭발물의 이격 거리를 통해 평가하여 내진 상세 적용 시 폭발 저항 성능이 향상된다는 것을 입증하였다.

• 대한물리치료과학회지
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• 제30권3호
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• pp.1-13
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• 2023

Background: The bridge exercise prevents repeated damage to the tissues around the spine by reducing stimulus transmission to the ligaments and joint capsules, thereby alleviating back pain. It also contributes to strengthening the muscles of the lower extremities. Design: A Single Subject experience design. Methods: This study was conducted on 28 healthy adults in their 20s to 30s and conducted at St. Mary's Hospital in C City from May to July 2021. Four types of bridge exercise were performed in this study: the normal bridge exercise and bridge exercises with 0.5%, 1%, or 1.5% body weight resistance applied on the pelvis through manual resistance during the bridge exercise and to determine the effect of resistance applied in the bridge exercise on the activation of the trunk and lower extremities muscles. Results:This study showed that the muscle activity of the trunk and lower extremities improved significantly in response to stronger resistance when manual resistance equivalent to 0.5%, 1%, or 1.5% of body weight was applied during the bridge exercise compared to when the normal bridge exercise was performed. Conclusion: This study shows that manual resistance can be applied as an effective method of bridge exercise since muscle activity in the trunk and lower extremities increases when manual resistance causing isometric contraction is applied.

• 전산구조공학
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• 제3권4호
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• pp.123-132
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• 1990

일반적으로 구조물의 내진설계에 있어서는 등가정적해석법이 주로 사용되고 있다. 현재 사용되고 있는 등가정적해석법은 구조물의 거동이 주로 기본진동 모드에 의해 지배된다는 가정하에 유도되었으므로 기본진동 주기가 긴 구조물에 대해서는 구조물의 동적특성을 정확하게 예측하기가 어렵다. 본 연구에서는 구조물의 설계시 직접적인 영향을 미치게 되는 층전단력의 분포를 주요 관점으로하여 구조물의 동적특성에 미치는 고차모드의 영향을 정확히 고려할 수 있는 층지진하중에 대하여 연구했다. 층지진하중의 분포를 개선하기 위해 현행 내진설계 기준의 등가정적해석법에서 쓰이는 층지진하중과 모드해석을 이용하여 얻은 층지진하중의 차이를 파악하고 이로부터 고차모드의 영향이 고려된 층지진하중의 분포를 제안했다.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.485-505
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• 2014

This study aimed to develop an approach to accurately predict the wind models and wind effects of large wind turbines. The wind-induced vibration characteristics of a 5 MW tower-blade coupled wind turbine system have been investigated in this paper. First, the blade-tower integration model was established, which included blades, nacelle, tower and the base of the wind turbine system. The harmonic superposition method and modified blade element momentum theory were then applied to simulate the fluctuating wind field for the rotor blades and tower. Finally, wind-induced responses and equivalent static wind loads (ESWL) of the system were studied based on the modified consistent coupling method, which took into account coupling effects of resonant modes, cross terms of resonant and background responses. Furthermore, useful suggestions were proposed to instruct the wind resistance design of large wind turbines. Based on obtained results, it is shown from the obtained results that wind-induced responses and ESWL were characterized with complicated modal responses, multi-mode coupling effects, and multiple equivalent objectives. Compared with the background component, the resonant component made more contribution to wind-induced responses and equivalent static wind loads at the middle-upper part of the tower and blades, and cross terms between background and resonant components affected the total fluctuation responses, while the background responses were similar with the resonant responses at the bottom of tower.

• Journal of Computing Science and Engineering
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• 제8권3호
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• pp.129-136
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• 2014

This paper presents the equivalent circuit modelling and eigenfrequency analysis of a wideband robust capacitive radio frequency (RF) microelectromechanical system (MEMS) switch that was designed using Poly-Si and Au layer membrane for highly reliable switching operation. The circuit characterization includes the extraction of resistance, inductance, on and off state capacitance, and Q-factor. The first six eigenfrequencies are analyzed using a finite element modeler, and the equivalent modes are demonstrated. The switch is optimized for millimeter wave frequencies, which indicate excellent RF performance with isolation of more than 55 dB and a low insertion loss of 0.1 dB in the V-band. The designed switch actuates at 13.2 V. The R, L, C and Q-factor are simulated using Y-matrix data over a frequency sweep of 20-100 GHz. The proposed switch has various applications in satellite communication networks and can also be used for devices that will incorporate the upcoming IEEE Wi-Fi 802.11ad protocol.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권1호
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• pp.43-49
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• 2005

The high rate of voltage rise (dv/dt) in motor terminals caused by high-frequency switching and impedance mismatches between inverter and motor are known as the primary causes of irregular voltage distributions and insulation breakdowns on stator windings in IGBT PWM inverter-driven induction motors. In this paper, voltage distributions in the stator windings of an induction motor driven by an IGBT PWM inverter are studied. To analyze the irregular voltages of stator windings, high frequency parameters are derived from the finite element (FE) analysis of stator slots. An equivalent circuit composed of distributed capacitances, inductance, and resistance is derived from these parameters. This equivalent circuit is then used for simulation in order to predict the voltage distributions among the turns and coils. The effects of various rising times in motor terminal voltages and cable lengths on the stator voltage distribution are also presented. For a comparison with simulations, an induction motor with taps in the stator turns was made and driven by a variable-rising time switching surge generator. The test results are shown.

• KIEE International Transactions on Electrophysics and Applications
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• 제2C권5호
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• pp.246-252
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• 2002

Two-dimensional steady state simulations of planar type radio frequency inductively coupled plasma (RFICP) have been performed. The characteristics of RFICP were investigated in terms of power transfer efficiency, equivalent circuit analysis, spatial distribution of plasma density and electron temperature. Plasma density and electron temperature were determined from the equations of ambipolar diffusion and energy conservation. Joule heating, ionization, excitation and elastic collision loss were included as the source terms of the electron energy equation. The electromagnetic field was calculated from the vector potential formulation of ampere's law. The peak electron temperature decreases from about 4eV to 2eV as pressure increases from 5 mTorr to 100 mTorr. The peak density increases with increasing pressure. Electron temperatures at the center of the chamber are almost independent of input power and electron densities linearly increase with power level. The results agree well with theoretical analysis and experimental results. A single turn, edge feeding antenna configuration shows better density uniformity than a four-turn antenna system at relatively low pressure conditions. The thickness of the dielectric window should be minimized to reduce power loss. The equivalent resistance of the system increases with both power and pressure, which reflects the improvement of power transfer efficiency.

• 한국환경보건학회지
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• 제21권4호
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• pp.24-31
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• 1995

Gas sensing element, $\alpha-Fe_2O_3$ was synthesized by dehydration, reduction, and oxidation of $\alpha-FeOOH$, which was synthesized with $FeSO_4\cdot 7H_2O$ and NaOH. They were produced as a bulk-type, a thick film-type. Then, their responses and mechanisms of response to the gas of carbon monoxide were studied. The qualities of gas sefising elements are decided by the structure and the relative surface area. In the process of $\alpha-FeOOH$ synthesis, the effects of reaction conditions as the equivalent ratio, on the structure and the relative surface area of gas sensing element were observed. The changes of the structure were measured with XRD, SEM,TG-DTA and BET. The resistance changes of the synthesized gas sensor in the air were measured. The response ratio were also measured for the changes of working temperature and gas concentration. As a result of analysis with XRD, it was confirmed that the the best conditions for the synthesis of $\alpha-FeOOH$ were equivalent ratio 0.65. The thick film-type element of $\gamma-Fe_2O_3$ responded more quickly than the bulk-type did. The structure and the relative surface area of the $\rho-FeOOH$ were confirmed as the important factors deciding gas response charcteristics.

• 한국소음진동공학회논문집
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• 제22권9호
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• pp.896-902
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• 2012

For most applications of the vibration energy harvesting technology as in wireless sensor networks for smart buildings and plants, the evaluation of DC output performance of vibration energy harvesters is typically required. However, there is no dedicated algorithm for the evaluation. The lack of a dedicated algorithm results from difficulties in the direct incorporation of nonlinear rectifying and regulating circuitry into finite element models of piezoelectric vibration energy harvesters. In this study, we develop a dedicated algorithm and present software based on it for the evaluation of not only AC but also DC electrical quantities. Here, an equivalent electrical circuit model is employed. The COMSOL multiphysics simulation tool is adopted for extracting equivalent electrical circuit parameters of a piezoelectric vibration energy harvester and MATLAB is used to make a graphical user interface. The AC voltage and power outputs calculated by the proposed algorithm under various conditions are compared with those by a traditional finite element analysis. The DC output voltage and power through a rectifier are obtained for varying values of smoothing capacitance and external resistance.