• Structural Monitoring and Maintenance
• /
• 제4권3호
• /
• pp.221-236
• /
• 2017

In this study, the feasibility of vibration-based damage alarming algorithms are numerically evaluated for wind turbine tower structures which are subjected to harmonic force excitation. Firstly, the algorithm of vibration-based damage alarming for the wind turbine tower (WTT) is visited. The natural frequency change, modal assurance criterion (MAC) and frequency-response-ratio assurance criterion (FRRAC) are utilized to recognize changes in dynamic characteristics due to a structural damage. Secondly, a finite element model based on a real wind turbine tower is established in a structural analysis program, Midas FEA. The harmonic force is applied at the rotor level as presence of excitation. Several structural damage scenarios are numerically simulated in segmental joints of the wind turbine model. Finally, the natural frequency change, MAC and FRRAC algorithm are employed to identify the structural damage occurred in the finite element model. The results show that these criteria could be used as promising damage existence indicators for the damage alarming in wind turbine supporting structures.

• Smart Structures and Systems
• /
• 제18권3호
• /
• pp.501-523
• /
• 2016

Electromechanical impedance (EMI) based structural health monitoring is performed by measuring the variation in the impedance due to the structural local damage. The impedance signals are acquired from the piezoelectric patches that are bonded on the structural surface. The impedance variation, which is directly related to the mechanical properties of the structure, indicates the presence of local structural damage. Two traditional EMI-based damage detection methods are based on calculating the difference between the measured impedance signals in the frequency domain from the baseline and the current structures. In this paper, a new structural damage detection approach by analyzing the time domain impedance responses is proposed. The measured time domain responses from the piezoelectric transducers will be used for analysis. With the use of the Time Frequency Autoregressive Moving Average (TFARMA) model, a damage index based on Singular Value Decomposition (SVD) is defined to identify the existence of the structural local damage. Experimental studies on a space steel truss bridge model in the laboratory are conducted to verify the proposed approach. Four piezoelectric transducers are attached at different locations and excited by a sweep-frequency signal. The impedance responses at different locations are analyzed with TFARMA model to investigate the effectiveness and performance of the proposed approach. The results demonstrate that the proposed approach is very sensitive and robust in detecting the bolt damage in the gusset plates of steel truss bridges.

• 조명전기설비학회논문지
• /
• 제18권4호
• /
• pp.83-87
• /
• 2004

본 논문에서는 Magnetic Levitation Model 시스템을 이용하여 선형 액추에이터의 기본모델을 제안하고 전원 공급부의 입력 주파수의 변화로부터 액추에이터에 나타나는 현상을 Matlab프로그램을 활용하여 간접적 방법으로 고찰하였다. 그 결과는 실제적인 설계에 적용할 경우 설계 프로그램의 자료나 부분적 변경 시 참조 할 수 있으리라 사료된다. 본 논문에서 제안한 에너지 변환을 고려한Linear Actuator M3d진 시스템의 출력은 입력 주파수의 변화로부터 액추에이터가 고주파보다는 저주파에서 권선부에 나타나는 파형의 응답이 기준 입력파형에 더 근접함을 알 수 있었다. 이 결과를 바탕으로 Linear Actuator Model 시스템의 동작 시 특성이 실제 시스템에 활용할 때 간접적 방법으로 상당히 유용함을 확인 할 수 있었다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2003년도 ICCAS
• /
• pp.1398-1403
• /
• 2003

In this paper, a simple method to design an MIMO sound field control system was proposed. The control system was designed to achieve 1) noise attenuation and 2) sound equalization by utilizing feedback and feedforward controllers. The method was based on partial model matching on frequency domain which only required measured frequency response data, or impulse response data in order to tune parameters of the controller. The proposed method was applied to a normal office room and results of experiment showed effectiveness of the proposed method.

• Journal of Magnetics
• /
• 제21권3호
• /
• pp.431-436
• /
• 2016

In the design of transformer winding, natural vibration frequency is an important parameter. This paper presents a 2D model to calculate axial vibration natural frequency of power transformer winding based on the elastic dynamics theory, and according to the elastic support equivalent principle of radial pressboards. The 3D model to calculate natural vibration frequency can be simplified as a 2D one as the support of pressboards on the winding is same. It is verified that results of the 2D model are consistent with those of 3D one, but the former can achieve much higher calculation efficiency. It shows that increasing the width and number of pressboards can improve axial natural frequency through formula analysis and simulation, and also the relations between the changes of axial pre-compression and axial natural vibration frequency on the windings are investigated. Finally, the proposed 2D model's effectiveness is proved when compared with tested ones.

• 대한전자공학회논문지SP
• /
• 제48권5호
• /
• pp.109-114
• /
• 2011

본 논문에서는 청각장애인을 위한 음향 데이터를 이용한 음향강화 알고리즘을 Gaussian Mixture Model (GMM)을 이용한 상황인지 시스템 기반으로 제안한다. 음향 신호 데이터에서 Mel-Frequency Cepstral Coefficients (MFCC) 특징벡터를 추출하여 GMM을 구성하고 이를 기반으로 상황인지 결과에 따라 위험음향일 경우 음향강화기술을 제안한다. 실험결과 제안된 상황인지 기반의 음향강화 알고리즘이 다양한 음향학적 환경에서 우수한 성능을 보인 것을 알 수 있었다.

• 한국소음진동공학회논문집
• /
• 제21권4호
• /
• pp.374-383
• /
• 2011

A numerical model based on a mode method coupling beams and a rectangular plate is proposed to estimate radiation characteristics of an edge-clamped rectangular plate. The radiation efficiency and radiation power in the audio frequency range including the critical frequency can be predicted. The proposed model is rather simple and straightforward and gives reliable results comparing to the previous studies. The estimated radiation characteristics are compared to those of the pinned condition plates and also to those based on the formulae proposed by Maidanik. The radiation efficiency of the clamped plate seems a little higher than that of the pinned plate in the frequency range of corner and edge modes. It is explicitly shown that the power as well as efficiency at high frequencies is not influenced by these edge boundary conditions.

• 한국소음진동공학회논문집
• /
• 제14권9호
• /
• pp.801-810
• /
• 2004

Parameter modification of a linear finite element model(FEM) based on modal sensitivity matrix is usually performed through an effort to match FEM modal data to experimental ones. However, there are cases where this method can't be applied successfully; lack of reliable modal data and ill-conditioning of the modal sensitivity matrix constitute such cases. In this research, a novel concept of introducing feedback loops to the conventional modal test setup is proposed. This method uses closed-loop natural frequency data for parameter modification to overcome the problems associated with the conventional method based on modal sensitivity matrix. We proposed the whole procedure of parameter modification using the closed-loop natural frequency data including the modal sensitivity modification and controller design method. Proposed controller design method is efficient in changing modes. Numerical simulation of parameter estimation based on time-domain input/output data is provided to demonstrate the estimation performance of the proposed method.

• Water Engineering Research
• /
• 제1권1호
• /
• pp.11-23
• /
• 2000

Regional flood frequency analysis has been developed by employing the nearby site's information to improve a precision in estimating flood quantiles at the site of interest. In this paper, single site and regional flood frequency analyses were compared based of the 2-parameter Weibull model. For regional analysis, two approaches were employed. The First one is to use the asymptotic variances of the quantile estimators derived based of the assumption that all sites including the site of interest are independent each other. This approach may give the maximum regional gain due to the spatial independence assumption among sites. The second one in Hosking's regional L-moment algorithm. These methods were applied to annual flood data. As the results, both methods generally showed the regional gain at the site of interest depending on grouping the sites as homogeneous. And asymptotic formula generally shows smaller variance than those from Hosking's algorithm. If the shape parameter of the site of interest from single site analysis is quite different from that from regional analysis then Hosking's results might be better than the asymptotic ones because the formula was derived based on the assumption that all sites have the same regional shape parameter. Furthermore, in such a case, regional analysis might be worse than single site analysis in the sense of precision of flood quantile estimation. Even though the selected sites may satisfy Hosking's criteria, regional analysis may not give a regional gain for specific and nonexceedance probabilities.

• 산업기술연구
• /
• 제27권A호
• /
• pp.47-53
• /
• 2007

A theoretical model based on Rayleigh-Ritz method is proposed to predict the resonance frequency of a W/T(Wind Turbine) tower structure supported by guy cables. In order to verify the validity of the theoretical model, a reduced W/T tower system is manufactured and tested. Frequency response and mode data are determined by modal testing and finite element analysis is performed to calculate the natural frequency of the tower model. Numerical and experimental results are compared with those by the theoretical analysis. Parametric study by the theoretical model shows how the cable tension and cable elasticity influence the resonance frequency of the W/T tower structure. Finally, vibration response under various rotating speed is investigated to examine the possibility of severe resonance.