• 한국공간구조학회논문집
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• 제13권1호
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• pp.79-86
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• 2013

For most of recent tall buildings, one characteristic is that their building shapes vary with height such as taper and setback, and this implies that the distribution of their structural components may also vary with height. Because of these structural variations, although the sectional shapes of these buildings are symmetric, it is difficult to say whether or not they are structurally symmetric. The acceleration responses of structurally asymmetric tall buildings are larger than those of non-eccentric buildings, thus raising the possibility of problems during strong winds and typhoons. This paper describes wind tunnel tests carried out using building models with height variations and acceleration response analyses, and discusses the resulting response characteristics. For tapered and setback buildings, although the across-wind accelerations are larger than those of a square building, the total root-mean-square accelerations remain small because of smaller along-wind and torsional rms accelerations. And it was found that the effects of statistical couplings between along-wind force and other two forces are negligible.

• 한국항공우주학회지
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• 제33권5호
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• pp.28-33
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• 2005

이선형 플런지 스프링을 가지는 2차원 단면 익형 모델에 대하여 초음속 비선형 공탄성 해석을 수행하였다. 초음속 비정상 공기력 계산을 위해 DPM을 사용하였고 최소상태접근법을 사용하여 근사하였다. 비선형 플러터 해석을 위해 구조 비선형성을 비대칭 이선형 스프링으로 모델링하고 기술 함수 법을 사용하여 선형화하였다. 선형 및 비선형 플러터 해석 결과들은 공력탄성학적 특성들이 주파수 비에 중요한 영향을 받는다는 것을 보여준다. 비선형 플러터 해석으로부터 다양한 제한 주기 운동이 선형플러터 속도 이하 또는 이상에서 관측되었다. 또한 플러터 특성과 응답을 시간영역에서도 조사하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.90-96
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• 2008

Engineered mixtures composed of rigid sand particles and soft rubber particles are tested to investigate their behavior with strain level. Mixtures are prepared with different volumetric sand fractions (sf) to identify response using small strain resonant column, intermediate strain oedometer, and large strain direct shear tests. The small strain shear modulus and damping ratio are determined with volumetric sand fractions. The asymmetric frequency response curve increases with decreasing sand fraction. Linear responses of shear strain and damping ratio with shear strain are observed at the mixture of sf=0.2. Vertical strain increases with decreasing sand fraction. Mixtures with $04.{\leq}sf{\leq}0.6$ show the transitional stress-deformation behavior from rubber-like to sand-like behavior. The friction angle increases with the sand fraction and no apparent peak strength is observed in mixture without sf=1.0.

• ETRI Journal
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• 제36권1호
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• pp.116-123
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• 2014

In this paper, a novel unequal broadband out-of-phase power divider (PD) is presented. Double-sided parallel-strip lines (DSPSLs) are employed to achieve an out-of-phase response. Also, an asymmetric dual-band matching structure with two external isolation resistors is utilized to obtain arbitrary unequal power division, in which the resistors are directly grounded for heat sinking. A through ground via (TGV), connecting the top and bottom sides of the DSPSLs, is used to short the isolation components. Additionally, this property can efficiently improve the broadband matching and isolation bandwidths. To investigate the proposed divider in detail, a set of design equations are derived based on the circuit theory and transmission line theory. The theoretical analysis shows that broadband responses can be obtained as proper frequency ratios are adopted. To verify the proposed concept, a sample divider with a power division of 2:1 is demonstrated. The measured results exhibit a broad bandwidth from 1.19 GHz to 2.19 GHz (59.2%) with a return loss better than 10 dB and port isolation of 18 dB.

• 소음진동
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• 제9권5호
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• pp.1019-1028
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• 1999

Free vibration characteristics of cantilevered laminated composite beams with a transverse non0propagating open carck are investigated. In the present analysis a special ply-angle distribution referred to as asymmetric stiffness configuration inducing the elastic coupling between chord-wise bending and extension is considered. The open crack is modelled as an equivalent rotational spring whose spring constant is calculated on the basis of fracture mechanics of composite material structures. Governing equations of a composite beam with a open crack are derived via Hamilton's Principle and Timoshenko beam theory encompassing transverse shear and rotary inertia effect. the effects of various parameters such as the ply angle, fiber volume fraction, crack depth, crack position and transverse shear on the free vibration characteristics of the beam with a crack is highlighted. The numerical results show that the natural frequencies obtained from Timoshenko beam theory are always lower than those from Euler beam theory. The presence of intrinsic cracks in anisotropic composite beams modifies the flexibility and in turn free vibration characteristics of the structures. It is revealed that non-destructive crack detection is possible by analyzing the free vibration responses of a cracked beam.

• 한국전산구조공학회논문집
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• 제15권3호
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• pp.421-432
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• 2002

본 연구에서는 진동제어를 목적으로 강성이 평면에서 비대칭적으로 분포된 구조물에 감쇠기를 설치할 경우 감쇠편심과 강성편심에 따른 모드특성 및 변위응답의 변화에 관하여 연구하였다 모드 특성으로는 고유진동수, 모드 감쇠비, 모드참여계수, 동적 증폭계수 등의 변화를 분석하였으며, 변위는 지진이력에 대한 약변, 강변, 무게중심 등에서의 변위를 비교하였다. 또한 이를 바탕으로 비틀림 응답을 최소화하기 위한 감쇠기의 적정 감쇠 편심 및 적정 감쇠 분배 문제에 대해 논하였으며, 단층구조물에서 유도된 적정 감쇠분배 방법을 다층구조뭍에 적용하고 그 효과를 확인하였다.

• 한국전산구조공학회논문집
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• 제34권3호
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• pp.121-128
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• 2021

본 연구에서는 비틀림비정형성과 수직비정형성을 가진 RC 필로티 건축물의 지진동에 대한 거동을 층강성을 적용하여 간단하게 모델링하는 선형 동적해석 프로그램을 개발하고자 한다. 개발된 동적 해석 프로그램을 적용하여 필로티 건축물의 동적 거동 및 필로티층 각 기둥의 전단력을 분석하고, 필로티층에 전단벽 또는 가새를 보강하였을 때 보강효과를 평가하고자 한다. 모서리코어가 있는 필로티 건축물에서 필로티층의 코어 반대편 모서리를 전단벽이나 K형 가새로 보강하였을 때 변위와 기둥 전단력이 크게 감소하는 것으로 나타났으며, 모서리 양면을 K형 가새로 보강하는 것보다 한 면을 전단벽으로 보강하는 것이 보강효과가 큰 것으로 나타났다.

• 유통과학연구
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• 제11권10호
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• pp.73-79
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• 2013

Purpose - This study examines the impact of oil price volatility on economic activities in Korea. The new millennium has seen a deregulation in the crude oil market, which invited immense capital inflow into Korea. It has also raised oil price levels and volatility. Drawing on the recent theoretical literature that emphasizes the role of volatility, this paper attends to the asymmetric changes in economic growth in response to the oil price movement. This study further examines several key macroeconomic variables, such as interest rate, production, and inflation. We come to the conclusion that oil price volatility can, in some part, explain the structural changes. Research design, data, and methodology - We use two methodological frameworks in this study. First, in regards to the oil price uncertainty, we use an Exponential-GARCH (Exponential Generalized Autoregressive Conditional Heteroskedasticity: EGARCH) model estimate to elucidate the asymmetric effect of oil price shock on the conditional oil price volatility. Second, along with the estimation of the conditional volatility by the EGARCH model, we use the estimates in a VECM (Vector Error Correction Model). The study thus examines the dynamic impacts of oil price volatility on industrial production, price levels, and monetary policy responses. We also approximate the monetary policy function by the yield of monetary stabilization bond. The data collected for the study ranges from 1990: M1 to 2013: M7. In the VECM analysis section, the time span is split into two sub-periods; one from 1990 to 1999, and another from 2000 to 2013, due to the U.S. CFTC (Commodity Futures Trading Commission) deregulation on the crude oil futures that became effective in 2000. This paper intends to probe the relationship between oil price uncertainty and macroeconomic variables since the structural change in the oil market became effective. Results and Conclusions - The dynamic impulse response functions obtained from the VECM show a prolonged dampening effect of oil price volatility shock on the industrial production across all sub-periods. We also find that inflation measured by CPI rises by one standard deviation shock in response to oil price uncertainty, and lasts for the ensuing period. In addition, the impulse response functions allude that South Korea practices an expansionary monetary policy in response to oil price shocks, which stems from oil price uncertainty. Moreover, a comparison of the results of the dynamic impulse response functions from the two sub-periods suggests that the dynamic relationships have strengthened since 2000. Specifically, the results are most drastic in terms of industrial production; the impact of oil price volatility shocks has more than doubled from the year 2000 onwards. These results again indicate that the relationships between crude oil price uncertainty and Korean macroeconomic activities have been strengthened since the year2000, which resulted in a structural change in the crude oil market due to the deregulation of the crude oil futures.

• Steel and Composite Structures
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• 제34권5호
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• pp.699-713
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• 2020

The aerodynamic performance of long-span cable-stayed bridges is much dependent on its geometrical configuration and countermeasure strategies. In present study, the aerodynamic performance of three composite cable-stayed bridges with different tower configurations and passive aerodynamic countermeasure strategies is systematically investigated by conducting a series of wind tunnel tests in conjunction with theoretical analysis. The structural characteristics of three composite bridges were firstly introduced, and then their stationary aerodynamic performance and wind-vibration performance (i.e., flutter performance, VIV performance and buffeting responses) were analyzed, respectively. The results show that the bridge with three symmetric towers (i.e., Bridge I) has the lowest natural frequencies among the three bridges, while the bridge with two symmetric towers (i.e., Bridge II) has the highest natural frequencies. Furthermore, the Bridge II has better stationary aerodynamic performance compared to two other bridges due to its relatively large drag force and lift moment coefficients, and the improvement in stationary aerodynamic performance resulting from the application of different countermeasures is limited. In contrast, it demonstrates that the application of both downward vertical central stabilizers (UDVCS) and horizontal guide plates (HGP) could potentially significantly improve the flutter and vortex-induced vibration (VIV) performance of the bridge with two asymmetric towers (i.e., Bridge III), while the combination of vertical interquartile stabilizers (VIS) and airflow-depressing boards (ADB) has the capacity of improving the VIV performance of Bridge II.

• 전력전자학회논문지
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• 제17권3호
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• pp.238-245
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• 2012

This paper presents a sensorless speed control of a 2-phase switch reluctance motor(SRM). The proposed sensorless control scheme is based on the slide mode observer with parameter compensator to improve the estimation performance. In the stand still position, the initial rotor position is determined by pulse current responses of each phase windings and the current difference. In order to determine an accurate initial rotor position, the two initial rotor positions are estimated by the difference of the pulse currents. From the stand still to the operating region, a simple open loop control which determines the commutation sequence by the pulse current of the unexcited phase winding is used. When the motor speed is reached to the sensorless control region, the estimated rotor position and speed by the slide mode observer are used to control the SRM. The flux calculator used in the slide mode observer is designed by phase voltage and the voltage drops in the phase resistance of the winding. The accuracy of the flux calculator is dependent on the phase resistance. For the continuous update of the phase resistance, current gradient at the inductance break point is used in this paper. The error of the estimated rotor position at the current gradient position is used to update the phase resistance to improve the sensorless scheme. The proposed sensorless speed control scheme is verified with a practical compressor used in home appliances. And the results show the effectiveness of the proposed control scheme.