Robust stability analysis of real-time hybrid simulation considering system uncertainty and delay compensation

Pei-Ching Chen,Po-Chang Chen 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.6

Real-time hybrid simulation (RTHS) which combines physical experiment with numerical simulation is an advanced method to investigate dynamic responses of structures subjected to earthquake excitation. The desired displacement computed from the numerical substructure is applied to the experimental substructure by a servo-hydraulic actuator in real time. However, the magnitude decay and phase delay resulted from the dynamics of the servo-hydraulic system affect the accuracy and stability of a RTHS. In this study, a robust stability analysis procedure for a general single-degree-of-freedom structure is proposed which considers the uncertainty of servo-hydraulic system dynamics. For discussion purposes, the experimental substructure is a portion of the entire structure in terms of a ratio of stiffness, mass, and damping, respectively. The dynamics of the servo-hydraulic system is represented by a multiplicative uncertainty model which is based on a nominal system and a weight function. The nominal system can be obtained by conducting system identification prior to the RTHS. A first-order weight function formulation is proposed which needs to cover the worst possible uncertainty envelope over the frequency range of interest. Then, the Nyquist plot of the perturbed system is adopted to determine the robust stability margin of the RTHS. In addition, three common delay compensation methods are applied to the RTHS loop to investigate the effect of delay compensation on the robust stability. Numerical simulation and experimental validation results indicate that the proposed procedure is able to obtain a robust stability margin in terms of mass, damping, and stiffness ratio which provides a simple and conservative approach to assess the stability of a RTHS before it is conducted.

The Loss Calculation of RCD Snubber with Forward and Reverse Recovery Effects Considerations

Chen Cai,Pei Xue-jun,Chen Yu,Kang Yong 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper addresses the problem of turn-off and turn-on performances of a RCD snubber circuit in high power inverter that works with insulated gate bipolar transistor (IGBT). The RCD snubber circuit turn-off and turn-on dynamics, forward and reverse recovery effects of the associated freewheeling and snubber diodes, and corresponding snubber losses are analyzed. Voltage impacts occur across the snubber resistor due to the snubber diode’s forward and reverse recovery effects, which bring in additional snubber losses. The turn-on current rising rates have two parts due to the anti-parallel free-wheeling diode (FWD) reverse recovery current that will influence the RCD loss. Moreover, the snubber has the same clamping effect as turn-off due to the anti-parallel FWD’s reverse recovery current. In addition, the proposed analysis was experimentally verified, the snubber loss are presented and discussed in the paper. Moreover, a well-designed temperature measurement is proposed to evaluate the loss.

Real-time hybrid simulation of smart base-isolated raised floor systems for high-tech industry

Pei-Ching Chen,Shiau-Ching Hsu,You-Jin Zhong,Shiang-Jung Wang 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.23 No.1

Adopting sloped rolling-type isolation devices underneath a raised floor system has been proved as one of the most effective approaches to mitigate seismic responses of the protected equipment installed above. However, pounding against surrounding walls or other obstructions may occur if such a base-isolated raised floor system is subjected to long-period excitation, leading to adverse effects or even more severe damage. In this study, real-time hybrid simulation (RTHS) is adopted to assess the control performance of a smart base-isolated raised floor system as it is an efficient and cost-effective experimental method. It is composed of multiple sloped rolling-type isolation devices, a rigid steel platen, four magnetorheological (MR) dampers, and protected high-tech equipment. One of the MR dampers is physically tested in the laboratory while the remainders are numerically simulated. In order to consider the effect of input excitation characteristics on the isolation performance, the smart base-isolated raised floor system is assumed to be located at the roof of a building and the ground level. Four control algorithms are designed for the MR dampers including passive-on, switching, modified switching, and fuzzy logic control. Six artificial spectrum-compatible input excitations and three slope angles of the isolation devices are considered in the RTHS. Experimental results demonstrate that the incorporation of semi-active control into a base-isolated raised floor system is effective and feasible in practice for high-tech industry.

Color Congruency between Text and Graphics Improves Reading Fluency and Comprehension

Pei-Chen, Wang,Tsuei-Ju, Hsieh,Da-Lun, Tang 한국색채학회 2017 AIC 2017 Jeju Vol.2017 No.10

In layout design, color helps not only to decorate but also to index important messages across texts. In this study, we used eye movement data and a reading comprehension test to examine how different color schemes could affect reading behavior when applied in various infographics composed graphics and corresponding explanation text. Three types of infographics were designed: a tour map, a data diagram and an explanatory graph. Each infographic was varied in four coloring schemes that used in highlighting important messages mutually in the texts and the graphics within a infographic. The messages appear in both graphic and the explanatory text were colored in gray scale (no color highlights), a single red color, multiple colors congruently highlight the text and graphics, and multiple colors incongruently highlight the text and graphics. Twenty participants were recruited for the tests. Two-way ANOVA and analyses indicated that different coloring schemes of highlights in text and graphics would impact the readers comprehending process, as well as use different coloring schemes in different information types.

Microstructure and mechanical properties of carbon graphite composites reinforced by carbon nanofibers

Chen Yixing,Tu Chuanjun,Liu Yanli,Liu Ping,Gong Pei,Wu Guangning,Huang Xia,Chen Jian,Liu Tianhua,Jiang Jizhou 한국탄소학회 2023 Carbon Letters Vol.33 No.2

Renewed interest in the reinforced carbon graphite composites has intrigued the community in the advanced materials fields. In this work, we present a simple carbon nanofibers reinforced carbon graphite composites synthetic method by incorporating mixture of coal tar pitch, synthetic graphite, pitch coke and the dispersion liquid of carbon nanofibers via liquid-phase mixing process. The impact of carbon nanofiber utilization on the microstructures and mechanical properties of carbon graphite composites are studied systematically. The covalent surface modification of carbon nanofibers effectively improves its microstructure and thereby promotes the carbon graphite composites’ dispersion behavior. We propose that a small amount of carbon nanofibers could promote the carbonization process of carbon graphite composites, facilitating the densification of carbon graphite composites and reducing the undesired open porosity. The amount of 0.7 wt % of carbon nanofiber concentration allows the enhancement of bend and compressive strength of carbon graphite composites up to 36.50 MPa and 60.46 MPa, increased by 167.9% and 146.9% compared with the pure carbon graphite composite, respectively. Our findings can be rationalized due to the improvement in the mechanical strength of carbon graphite composites could be attributed due to pull-out of carbon nanofibers from the matrix and bridging effect across the crack pores within the matrix.

Performance-based optimization of LQR for active mass damper using symbiotic organisms search

Pei-Ching Chen,Bryan J. Sugiarto,Kai-Yi Chien 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.4

The linear-quadratic regulator (LQR) has been applied to structural vibration control for decades; however, selection of the weighting matrices of an LQR mostly depends on trial and error. In this study, a novel metaheuristic optimization method named as symbiotic organisms search (SOS) algorithm is applied to tuning LQR weighting matrices for active mass damper (AMD) control systems. A 10-story shear building with an active mass damper installed at the top is adopted as a benchmark for numerical simulation in order to realize the optimization performance considering three objective functions for mitigation of structural acceleration. Two common optimization methods including genetic algorithm (GA), and particle swarm optimization (PSO) are also applied to this benchmark for comparison purposes. Numerical simulation results indicate that SOS is superior to GA and PSO on searching the minimized solution of the three objective functions. Meanwhile, minimizing the square root of the sum of the squares of peak modal acceleration achieves the best control performance of structural acceleration among the three objective functions. In addition, force saturation is proposed and applied in the optimization process such that the control force level is close to the force capacity of AMD under specified earthquake intensity. Furthermore, the control performance of the optimized LQR is compared with that of the LQR designed by applying three common weighting selection methods when the 10-story building is subjected to various earthquake excitations. Simulation results demonstrate that the optimized LQR significantly outperforms the three LQRs on structural acceleration responses as expected and reduces story drift slightly better than the three LQRs. Finally, the performance-based optimized LQR is experimentally validated by conducting shake table testing in the laboratory. The experimental results and structural control performance are discussed and summarized thoroughly.

Screening and Evaluation of Yeast Antagonists for Biological Control of Botrytis cinerea on Strawberry Fruits

( Pei-hua Chen ),( Rou-yun Chen ),( Jui-yu Chou ) 한국균학회 2018 Mycobiology Vol.46 No.1

Gray mold (Botrytis cinerea) is one of the most common diseases of strawberries (Fragaria×ananassa Duchesne) worldwide. Although many chemical fungicides are used for controlling the growth of B. cinerea, the risk of the fungus developing chemical resistance together with consumer demand for reducing the use of chemical fungicides have necessitated an alternative method to control this pathogen. Various naturally occurring microbes aggressively attack plant pathogens and benefit plants by suppressing diseases; these microbes are referred to as biocontrol agents. However, screening of potent biocontrol agents is essential for their further development and commercialization. In this study, 24 strains of yeast with antagonistic ability against gray mold were isolated, and the antifungal activity of the volatile and diffusible metabolites was evaluated. Putative mechanisms of action associated with the biocontrol capacity of yeast strains against B. cinerea were studied through in vitro and in vivo assays. The volatile organic compounds produced by the Galactomyces candidum JYC1146 could be useful in the biological control of plant pathogens and therefore are potential alternative fungicides with low environmental impact.

Leaching characteristics and kinetics of the metal impurities present in rice husk during pretreatment for the production of nanosilica particles

Pei Chen,Haipei Bie,Rushan Bie 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.9

Fundamental studies on the removal of metal impurities are essential for the production of nanosilica by combustion. This study reports the leaching characteristics, leaching kinetics and occurrence form of the metal impurities present in rice husk based on acid pretreatment. Acid pretreatment removes most of the metal impurities present in rice husk. In particular, 98wt% removal of potassium can be reached. The acid concentration, leaching time and reagent type have significant effects on the leaching of metal impurities, and optimal conditions exist for the acid pretreatment process. Furthermore, the leaching of metal impurities occurs through two stages, and parts of the metal impurities exist in organic-bound form, which can be leached through ion exchange. The results show that the pseudosecond- order model is suitable for describing the leaching kinetics of the metal impurities present in rice husk, and empirical formulas for predicting the metal contents leached from rice husk during acid pretreatment at ambient temperature are also obtained. Additionally, the different occurrence form and quantities of metal impurities in rice husk lead to different leaching effects, which strongly influences the chemical properties and quality of the obtained silica particles.

A new phenotype of TUBB4A mutation in a family with adult-onset progressive spastic paraplegia and isolated hypomyelination leukodystrophy: A case report and literature review

Pei-Chen Hsieh,Yih-Ru Wu 대한파킨슨병및이상운동질환학회 2024 Journal Of Movement Disorders Vol.17 No.1

Tubulin beta 4A class IVa (TUBB4A) spectrum disorders include autosomal dominant dystonia type 4 or hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC syndrome). However, in rare cases, only mild hypomyelination in the cortex with no basal ganglia atrophy may be observed. We report a case of a family with TUBB4A mutation and complicated hereditary spasticity paraplegia (HSP). We performed quadro whole-exome sequencing (WES) on the family to identify the causative gene of progressive spastic paraparesis with isolated hypomyelination leukodystrophy. We identified a novel TUBB4A p.F341L mutation, which was present in all three affected patients but absent in the unaffected father. The affected patients presented with adult-onset TUBB4A disorder, predominant spastic paraparesis with/without ataxia, and brain hypomyelination with no cognitive impairment or extrapyramidal symptoms. In the literature, HSP is considered a TUBB4A spectrum disorder.

Servo control strategy for uni-axial shake tables using long short-term memory networks

Pei-Ching Chen,Kui-Xing Lai 국제구조공학회 2023 Smart Structures and Systems, An International Jou Vol.32 No.6

Servo-motor driven uniaxial shake tables have been widely used for education and research purposes in earthquake engineering. These shake tables are mostly displacement-controlled by a digital proportional-integral-derivative (PID) controller; however, accurate reproduction of acceleration time histories is not guaranteed. In this study, a control strategy is proposed and verified for uniaxial shake tables driven by a servo-motor. This strategy incorporates a deep-learning algorithm named Long Short-Term Memory (LSTM) network into a displacement PID feedback controller. The LSTM controller is trained by using a large number of experimental data of a self-made servo-motor driven uniaxial shake table. After the training is completed, the LSTM controller is implemented for directly generating the command voltage for the servo motor to drive the shake table. Meanwhile, a displacement PID controller is tuned and implemented close to the LSTM controller to prevent the shake table from permanent drift. The control strategy is named the LSTM-PID control scheme. Experimental results demonstrate that the proposed LSTM-PID improves the acceleration tracking performance of the uniaxial shake table for both bare condition and loaded condition with a slender specimen.