• Smart Structures and Systems
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• 제31권2호
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• pp.131-140
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• 2023

As well-known, the extended Kalman filter (EKF) is a powerful tool for parameter identification with limited measurements. However, traditional EKF is not applicable when the external excitation is unknown. By using least-squares estimation (LSE) for force identification, an EKF with unknown input (EKF-UI) approach was recently proposed by the authors. In this approach, to ensure the influence matrix be of full column rank, the sensors have to be deployed at all the degrees-of-freedom (DOFs) corresponding to the unknown excitation, saying collocated measurements are required. However, it is not easy to guarantee that the sensors can be installed at all these locations. To circumvent this limitation, based on the idea of first-order-holder discretization (FOHD), an improved EKF with unknown input (IEKF-UI) approach is proposed in this study for the simultaneous identification of structural parameters and unknown excitation. By using projection matrix, an improved observation equation is obtained. Few displacement measurements are fused into the observation equation to avoid the so-called low-frequency drift. To avoid the ill-conditioning problem for force identification without collocated measurements, the idea of FOHD is employed. The recursive solution of the structural states and unknown loads is then analytically derived. The effectiveness of the proposed approach is validated via several numerical examples. Results show that the proposed approach is capable of satisfactorily identifying the parameters of linear and nonlinear structures and the unknown excitation applied to them.

• 대한기계학회논문집A
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• 제26권12호
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• pp.2647-2655
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• 2002

This research presents an analytical model to investigate the stability due to the ball bearing waviness i n a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time -varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i=1,2,3..).

• Journal of the Optical Society of Korea
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• 제20권6호
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• pp.778-783
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• 2016

We synthesized $Er^{3+}-Yb^{3+}$, $Pr^{3+}-Yb^{3+}$, and $Er^{3+}-Pr^{3+}-Yb^{3+}$ -doped oxyfluoride glass ceramics containing $CaF_2$ nanocrystals by proper thermal treatments. Spectral characteristics of down- and up-converted emissions in three kinds of glass ceramics under 365-nm and 980-nm excitations were compared and explained by cross relaxations, excited-state absorptions, and energy-transfer processes between different ions. The huge reduction of up-conversion emission in the triply doped glass ceramics under 980-nm excitation compared to the $Er^{3+}-Yb^{3+}$ codoped one was explained by the split pump power and the direct energy transfer from $Er^{3+}$ to $Pr^{3+}$ ions. Increasing $Yb^{3+}$ concentration from 2% to 10% in the triply doped glass ceramics showed more than quadratic enhancement of the absorbed power, and we explained it by the enhanced energy-transfer efficiency from $Yb^{3+}$ to $Er^{3+}$ ions. We also observed enhanced up-converted emissions of $Er^{3+}$ and $Pr^{3+}$ ions in three kinds of glass ceramics under simultaneous excitation at 980 nm and 1550 nm, and suggested detailed up-conversion mechanisms.

• Smart Structures and Systems
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• 제15권1호
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• pp.169-189
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• 2015

Convergence difficulty and available complete measurement information have been considered as two primary challenges for the identification of large-scale engineering structures. In this paper, a time domain substructural identification approach by combining a weighted adaptive iteration (WAI) algorithm and an extended Kalman filter method with a weighted global iteration (EFK-WGI) algorithm was proposed for simultaneous identification of physical parameters of concerned substructures and unknown external excitations applied on it with limited response measurements. In the proposed approach, according to the location of the unknown dynamic loadings and the partially available structural response measurements, part of structural parameters of the concerned substructure and the unknown loadings were first identified with the WAI approach. The remaining physical parameters of the concerned substructure were then determined by EFK-WGI basing on the previously identified loadings and substructural parameters. The efficiency and accuracy of the proposed approach was demonstrated via a 20-story shear building structure and 23 degrees of freedom (DOFs) planar truss model with unknown external excitation and limited observations. Results show that the proposed approach is capable of satisfactorily identifying both the substructural parameters and unknown loading within limited iterations when both the excitation and dynamic response are partially unknown.

• BMB Reports
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• 제46권12호
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• pp.600-605
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• 2013

Interplay between calcium ions ($Ca^{2+}$) and reactive oxygen species (ROS) delicately controls diverse pathophysiological functions of vascular smooth muscle cells (VSMCs). However, details of the $Ca^{2+}$ and ROS signaling network have been hindered by the absence of a method for dual measurement of $Ca^{2+}$ and ROS. Here, a real-time monitoring system for $Ca^{2+}$ and ROS was established using a genetically encoded hydrogen peroxide indicator, HyPer, and a ratiometric $Ca^{2+}$ indicator, fura-2. For the simultaneous detection of fura-2 and HyPer signals, 540 nm emission filter and 500 nm~ dichroic beamsplitter were combined with conventional exciters. The wide excitation spectrum of HyPer resulted in marginal cross-contamination with fura-2 signal. However, physiological $Ca^{2+}$ transient and hydrogen peroxide were practically measurable in HyPer-expressing, fura-2-loaded VSMCs. Indeed, distinct $Ca^{2+}$ and ROS signals could be successfully detected in serotonin-stimulated VSMCs. The system established in this study is applicable to studies of crosstalk between $Ca^{2+}$ and ROS.

• Structural Engineering and Mechanics
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• 제56권5호
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• pp.871-897
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• 2015

This paper presents a novel method based on sensitivity of structural response for identifying both the system parameters and input excitation force of a bridge. This method, referred to as "Adjoint Variable Method", is a sensitivity-based finite element model updating method. The computational cost of sensitivity analyses is the main concern associated with damage detection by these methods. The main advantage of proposed method is inclusion of an analytical method to augment the accuracy and speed of the solution. The reliable performance of the method to precisely indentify the location and intensity of all types of predetermined single, multiple and random damages over the whole domain of moving vehicle speed is shown. A comparison study is also carried out to demonstrate the relative effectiveness and upgraded performance of the proposed method in comparison to the similar ordinary sensitivity analysis methods. Moreover, various sources of error including the effects of noise and primary errors on the numerical stability of the proposed method are discussed.

• 물과 미래
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• 제26권1호
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• pp.63-69
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• 1993

매립이 완료된 Landfills이나 오염된 지하수의 오염물질을 제거하여 다른 용도로 재사용하는 기술이 오늘날 중요한 문제로 대두되고 있다. 진동을 이용하여 제가효율을 높히는 방법은 요즘 흔히 사용되고 있는 방법중의 하나이다. Ultrasonic의 효과를 사용함으로써, 기계적인 제거효과가 대단하다는 것은 이미 몇몇 연구자들에 의해 확인된바 있다. 이 연구에서는 Probe-Type Lutrasonic Processor를 사용하여 Clayey-Sand Chamber를 가지고 실험을 해보았다. 실험중 계속적인 Pumping과 함께 Ultrasonic을 작동시킨 결과, Clayey 입자들의 분리 및 제거에 큰 효과를 얻었으며, 그로 인하여 투수계수가 크게 증가하는 효과를 보았다. 또한, 실험 전과 후의 입자크기의 분포도가 크게 변했는데, 그 이유는 Ultrasonic의 진동효과 때문이다. 실험결과, 0.004mm 이하의 입자들은 Ultrasonic의 효과에 의해 Mobilize되었으며, 0.04-1.0mm의 입자는 부서져서 작은 입자로 되었다. 이 기구를 사용하기 위한 유지비와 전력비등을 고려하여 이 기구의 실용성을 검토해 보았다. 필요한 Power를 위해 요구되는 전력의 양은 깊이에 의한 대상 site의 응력, 온도, 그리고 Fuid의 Viscosity에 의해 좌우되며, 그중 가장 큰 영향을 미치는 요소는 흙의 깊이이다. 여러 가지의 다른 깊이에서의 경제적인 실용성을 1.0, 2.0in 직경의 Horn Sonicator를 사용했을 경우에 대하여 비교와 분석을 하였다.

• Smart Structures and Systems
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• 제31권3호
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• pp.229-245
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• 2023

The absence of excitation measurements may pose a big challenge in the application of structural damage identification owing to the fact that substantial effort is needed to reconstruct or identify unknown input force. To address this issue, in this paper, an iterative strategy, a synergy of Tikhonov regularization method for force identification and modified Jaya algorithm (M-Jaya) for stiffness parameter identification, is developed for damage identification with partial output-only responses. On the one hand, the probabilistic clustering learning technique and nonlinear updating equation are introduced to improve the performance of standard Jaya algorithm. On the other hand, to deal with the difficulty of selection the appropriate regularization parameters in traditional Tikhonov regularization, an improved L-curve method based on B-spline interpolation function is presented. The applicability and effectiveness of the iterative strategy for simultaneous identification of structural damages and unknown input excitation is validated by numerical simulation on a 21-bar truss structure subjected to ambient excitation under noise free and contaminated measurements cases, as well as a series of experimental tests on a five-floor steel frame structure excited by sinusoidal force. The results from these numerical and experimental studies demonstrate that the proposed identification strategy can accurately and effectively identify damage locations and extents without the requirement of force measurements. The proposed M-Jaya algorithm provides more satisfactory performance than genetic algorithm, Gaussian bare-bones artificial bee colony and Jaya algorithm.

• 소음진동
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• 제7권1호
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• pp.143-152
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• 1997

This paper introduces experimental results of the ride qulaity characteristics of automotive seats fixed on the vibration table that is noving simultaneously to the three-axis in a similar way to the real running condition. Vibration experiment was carried out for five different automotive seats and four Korean individuals. The assessment of the ride quality characteristics for each seat and indiviual was made not only from the analysis of vibration measurements but also from the evaluation of weighied vibration signals, which were obtained using the frequency weighting function and the multiplication factor dependent on the position and axis of vibration exposure to wehole-body. The usefulness of those assessment results in analysis of the ride quality of seats is discussed and their limitation is also pointed out in this paper.

• 전기학회논문지
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• 제58권4호
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• pp.655-664
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• 2009

This paper, Part 1, describes the effective dual-input PSS parameter design procedure for the IEEE Type PSS2A against the Dangjin 612 MVA thermal plant's EX2000 excitation system. The suggested tuning technique used the model-based PSS tuning method and consisted of three steps: 1) generation system modeling; 2) determination of PSS2A model parameters using linear, time-domain transient and 3-phase simultaneous analyses, and 3) field testing and verification, which are described in Part 2. The effective PSS2A model parameters of EX2000 system in the Dangjin T/P #4 were designed according to the suggested procedure, and verified by using three analyses.