• 한국음향학회:학술대회논문집
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• 한국음향학회 2000년도 하계학술발표대회 논문집 제19권 1호
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• pp.411-414
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• 2000

음의 비선형 전파가 일어나기 쉬운 정도를 나타내는 파라메타로서 기본파 진폭과 제2고조파 진폭의 비로써 매질의 물리적 성질에만 관계하는 파라메타 B/A가 있다(1)(2). 종래 B/A파라메타 측정은 대부분 광대역의 초음파 트랜스듀서 혹은 공진 주파수가 다른 복수의 트랜스듀서를 이용하여 왔다(3). 본 연구에서는 협대역의 단일 트랜스듀서를 이용하여 B/A파라메타를 효율적으로 측정 할 수 있는 전용 초음파 트랜스듀서를 제안하였다. 그 방법으로 특성이 동일한 두 장의 압전체를 적층시키고, 그 중 한 장의 압전체에 전기적인 용량을 접속하여 기본 공진 모드 및 기본 공진 모드의 두 배의 주파수에 해당되는 조화파 모드를 발생시킬 수 있도록 하였다 이것을 시험 제작하여 그 특성을 이론 및 실험적으로 해석한 결과 음향 매질의 비선형 파라메타인 B/A의 측정에 적용 가능함을 확인하였다.

• Coupled systems mechanics
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• 제12권3호
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• pp.277-295
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• 2023

Unsymmetrical high-rise buildings (HRBs) subjected to earthquake represent a difficult challenge to structural engineering, especially taking into consideration the effect of soil-structure interaction (SSI). L-shape in plan HRBs suffer from big straining actions when are subjected to an earthquake (in x- or y-direction, or both x- and y- directions). Additionally, the disastrous effect of seismic pounding may appear between two adjacent unsymmetrical HRBs. For two unsymmetrical L-shape in plan HRBs subjected to earthquake in three different direction cases (x, y, or both), including the SSI effect, different methods are investigated to mitigate the seismic pounding and thus protect these types of structures under the earthquake effect. The most effective technique to mitigate the seismic pounding and help in seismically protecting these adjacent HRBs is found herein to be the use of a combination of pounding tuned mass dampers (PTMDs) all over the height (at the connection points) together with tuned mass dampers (TMDs) on the top of both buildings.

• 전력전자학회논문지
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• 제16권5호
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• pp.521-531
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• 2011

본 논문은 그림자 영향을 고려한 PV(Photovoltaic) 시스템의 VPO(Variable Perturbation & Observation)MPPT(Maximum Power Point Tracking) 제어를 제시한다. 태양전지의 출력 특성은 비선형이고 온도, 일사량 및 그림자의 영향을 많이 받는다. MPPT 제어는 태양광발전 시스템의 출력 및 효율을 증가시키기 위한 매우 중요한 기술이다. 종래의 PO(Perturbation & Observation)와 IC(Incremental conductance) 등은 지속적인 자려진동에 의해 MPP(Maximum Power Point)를 찾는 방법으로 그림자 영향에 의해 출력이 급격하게 변할 경우 MPPT 제어를 수행하지 못한다. 이러한 문제점을 해결하기 위해 출력 변동에 따라 스텝 값이 변하는 새로운 제어 알고리즘을 제시한다. 제시한 알고리즘은 일사량, 온도 및 그림자 영향에 대해 종래의 제어 알고리즘과 응답특성을 비교하고 이를 통해 제시한 알고리즘의 타당성을 입증한다.

• Smart Structures and Systems
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• 제23권5호
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• pp.449-466
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• 2019

Cable-stayed bridges are attractive due to their beauty, reducing material consumption, less harm to the environment and so on, in comparison with other kinds of bridges. As a massive structure with long period and low damping (0.3 to 2%) under many dynamic loads, these bridges are susceptible to fatigue, serviceability disorder, damage or even collapse. Tuned Mass Damper (TMD) is a suitable controlling system to reduce the vibrations and prevent the threats in such bridges. In this paper, Multi Tuned Mass Damper (MTMD) system is added to the Ahvaz cable stayed Bridge in Iran, to reduce its seismic vibrations. First, the bridge is modeled in SAP2000 followed with result verification. Dead and live loads and the moving loads have been assigned to the bridge. Then the finite element model is developed in OpenSees, with the goal of running a nonlinear time-history analysis. Three far-field and three near-field earthquake records are imposed to the model after scaling to the PGA of 0.25 g, 0.4 g, 0.55 g and 0.7 g. Two MTMD systems, passive and active, with the number of TMDs from 1 to 8, are placed in specific points of the main span of bridge, adding a total mass ratio of 1 to 10% to the bridge. The parameters of the TMDs are optimized using Genetic Algorithm (GA). Also, the optimum force for active control is achieved by Fuzzy Logic Control (FLC). The results showed that the maximum displacement of the center of the bridge main span reduced 33% and 48% respectively by adding passive and active MTMD systems. The RMS of displacement reduced 37% and 47%, the velocity 36% and 42% and also the base shear in pylons, 27% and 47%, respectively by adding passive and active systems, in the best cases.

• 한국지진공학회논문집
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• 제8권4호
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• pp.33-42
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• 2004

점탄성감쇠기 (VED)를 건물의 내부에 가새의 형태로 설치하는 기존의 방법은 공간 이용에 제약이 되며, 내부 동선을 방해할 수 있다. 이러한 단점은 VED를 건물사이의 신축이음부 (신축줄눈)나 지진줄눈 사이에 설치함으로써 해결할 수 있다. 본 연구에서는 신축이음부에 설치된 VED의 내진성능 향상 효과에 관하여 연구하였다. 이를 위하여 VED로 연결된 3자유도 구조물의 지진하중에 대한 각 설계 변수들의 효과를 파악하고, 제안된 방법의 실용성을 검토하였다. 이를 바탕으로 서로 다른 구조 시스템으로 설계된 5층 구조물을 VED로 연결하고 시간이력 해석을 수행하였다. 해석 결과에 따르면 인접한 구조물의 고유주기가 다르게 설계된 경우, VED로 연결된 구조물의 내진 성능을 상당히 향상할 수 있는 것으로 나타났다.

• 조명전기설비학회논문지
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• 제24권4호
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• pp.166-176
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• 2010

태양전지의 출력 특성은 비선형이고 온도와 일사량에 많은 영향을 받는다. 최대전력점 추종 제어는 태양광 발전의 출력을 최대로 하기 위해 사용되는 제어기법이다. 태양광발전 시스템의 출력 및 효율을 증가 시키기 위해 더욱 우수한 최대전력점 추종 제어기법이 필요하다. 본 논문에서는 태양광 발전 시스템의 효율을 개선하기 위해 일사량을 고려한 새로운 최대전력점 추종 제어 알고리즘을 제시한다. 제시한 알고리즘은 종래의 P&O방법과 CV 방법을 혼합한 것이며, PSIM 시뮬레이터를 통하여 종래의 MPPT 알고리즘과 다양한 일사량 조건에서 성능시험을 비교하였다. 제시한 알고리즘은 종래의 알고리즘에 비해 출력의 자려진동없이 다양한 일사량에서 우수한 성능을 나타냈다. 이로서 본 논문에서 제시한 HB 방법의 최대전력점 추종 제어 알고리즘의 타당성을 입증하였다.

• 항공우주시스템공학회지
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• 제14권3호
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• pp.69-77
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• 2020

본 논문에서는 35 kg급 재난치안용 멀티콥터 무인기의 기체구조 개발에 대해 기술한다. 경량화를 위해 구조재료는 T-700급 탄소 복합재료를 사용하였으며, 동체는 세미 모노코크 구조로, 제어 및 통신장비가 장착되는 판재는 샌드위치 구조로 설계하였다. 설계된 부품과 동일한 적층판과 파이프를 제작하고 시편시험을 수행하여 강도와 강성을 확인하였다. 정적강도 및 진동 해석을 수행하여 복합재료 적층순서를 결정하였고, 착륙속도 및 지상이격 요구조건과 비선형 해석을 통해 착륙장치 스트러트의 적층순서를 결정하였다. 정적강도시험을 통해 구조 건전성을 평가하고 착륙장치의 거동을 확인하였다.

• Smart Structures and Systems
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• 제30권1호
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• pp.75-88
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• 2022

Engineering structures in operation essentially belong to time-varying or nonlinear structures and the resultant response signals are usually non-stationary. For such time-varying structures, it is of great importance to extract time-dependent dynamic parameters from non-stationary response signals, which benefits structural health monitoring, safety assessment and vibration control. However, various traditional signal processing methods are unable to extract the embedded meaningful information. As a newly developed technique, variational mode decomposition (VMD) shows its superiority on signal decomposition, however, it still suffers two main problems. The foremost problem is that the number of modal components is required to be defined in advance. Another problem needs to be addressed is that VMD cannot effectively separate non-stationary signals composed of closely spaced or overlapped modes. As such, a new method named generalized adaptive variational modal decomposition (GAVMD) is proposed. In this new method, the number of component signals is adaptively estimated by an index of mean frequency, while the generalized demodulation algorithm is introduced to yield a generalized VMD that can decompose mode overlapped signals successfully. After that, synchrosqueezing wavelet transform (SWT) is applied to extract instantaneous frequencies (IFs) of the decomposed mono-component signals. To verify the validity and accuracy of the proposed method, three numerical examples and a steel cable with time-varying tension force are investigated. The results demonstrate that the proposed GAVMD method can decompose the multi-component signal with overlapped modes well and its combination with SWT enables a successful IF extraction of each individual component.

• Wind and Structures
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• 제34권2호
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• pp.173-183
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• 2022

The galloping of iced conductors has long been a severe threat to the safety of overhead transmission lines. Compared with normal transmission lines, the ultra-high-voltage (UHV) transmission lines are more prone to galloping, and the damage caused is more severe. To control the galloping of UHV lines, it is necessary to conduct a comprehensive analysis of galloping characteristics. In this paper, a large-span 1000-kV UHV transmission line in China is taken as a practical example where an 8-bundled conductor with D-shaped icing is adopted. Galerkin method is employed for the time history calculation. For the wind attack angle range of 0°~180°, the galloping amplitudes in vertical, horizontal, and torsional directions are calculated. Furthermore, the vibration frequencies and galloping shapes are analyzed for the most severe conditions. The results show that the wind at 0°~10° attack angles can induce large torsional displacement, and this range of attack angles is also most likely to occur in reality. The galloping with largest amplitudes in all three directions occurs at the attack angle of 170° where the incoming flow is at the non-iced side, due to the strong aerodynamic instability. In addition, with wind speed increasing, galloping modes with higher frequencies appear and make the galloping shape more complex, indicating strong nonlinear behavior. Based on the galloping amplitudes of three directions, the full range of wind attack angles are divided into five galloping regions of different severity levels. The results obtained can promote the understanding of galloping and provide a reference for the anti-galloping design of UHV transmission lines.

• Smart Structures and Systems
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• 제20권1호
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• pp.61-74
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• 2017

One of the most reliable and simplest tools for structural vibration control in civil engineering is Tuned Mass Damper, TMD. Provided that the frequency and damping parameters of these dampers are tuned appropriately, they can reduce the vibrations of the structure through their generated inertia forces, as they vibrate continuously. To achieve the optimal parameters of TMD, many different methods have been provided so far. In old approaches, some formulas have been offered based on simplifying models and their applied loadings while novel procedures need to model structures completely in order to obtain TMD parameters. In this paper, with regard to the nonlinear decision-making of fuzzy systems and their enough ability to cope with different unreliability, a method is proposed. Furthermore, by taking advantage of both old and new methods a fuzzy system is designed to be operational and reduce uncertainties related to models and applied loads. To design fuzzy system, it is required to gain data on structures and optimum parameters of TMDs corresponding to these structures. This information is obtained through modeling MDOF systems with various numbers of stories subjected to far and near field earthquakes. The design of the fuzzy systems is performed by three methods: look-up table, the data space grid-partitioning, and clustering. After that, rule weights of Mamdani fuzzy system using the look-up table are optimized through genetic algorithm and rule weights of Sugeno fuzzy system designed based on grid-partitioning methods and clustering data are optimized through ANFIS (Adaptive Neuro-Fuzzy Inference System). By comparing these methods, it is observed that the fuzzy system technique based on data clustering has an efficient function to predict the optimal parameters of TMDs. In this method, average of errors in estimating frequency and damping ratio is close to zero. Also, standard deviation of frequency errors and damping ratio errors decrease by 78% and 4.1% respectively in comparison with the look-up table method. While, this reductions compared to the grid partitioning method are 2.2% and 1.8% respectively. In this research, TMD parameters are estimated for a 15-degree of freedom structure based on designed fuzzy system and are compared to parameters obtained from the genetic algorithm and empirical relations. The progress up to 1.9% and 2% under far-field earthquakes and 0.4% and 2.2% under near-field earthquakes is obtained in decreasing respectively roof maximum displacement and its RMS ratio through fuzzy system method compared to those obtained by empirical relations.