Estimation of active multiple tuned mass dampers for asymmetric structures

Li, Chunxiang,Xiong, Xueyu Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.5

This paper proposes the application of active multiple tuned mass dampers (AMTMD) for translational and torsional response control of a simplified two-degree-of-freedom (2DOF) structure, able to represent the dynamic characteristics of general asymmetric structures, under the ground acceleration. This 2DOF structure is a generalized 2DOF system of an asymmetric structure with predominant translational and torsional responses under earthquake excitations using the mode reduced-order method. Depending on the ratio of the torsional to the translational eigenfrequency, i.e. the torsional to translational frequency ratio (TTFR), of asymmetric structures, the following three cases can be distinguished: (1) torsionally flexible structures (TTFR < 1.0), (2) torsionally intermediate stiff structures (TTFR = 1.0), and (3) torsionally stiff structures (TTFR > 1.0). The even distribution of the AMTMD within the whole width and half width of the asymmetric structure, thus leading to three cases of installing the AMTMD (referred to as the AMTMD of case 1, AMTMD of case 2, AMTMD of case 3, respectively), is taken into account. In the present study, the criterion for searching the optimum parameters of the AMTMD is defined as the minimization of the minimum values of the maximum translational and torsional displacement dynamic magnification factors (DMF) of an asymmetric structure with the AMTMD. The criterion used for assessing the effectiveness of the AMTMD is selected as the ratio of the minimization of the minimum values of the maximum translational and torsional displacement DMF of the asymmetric structure with the AMTMD to the maximum translational and torsional displacement DMF of the asymmetric structure without the AMTMD. By resorting to these two criteria, a careful examination of the effects of the normalized eccentricity ratio (NER) on the effectiveness and robustness of the AMTMD are carried out in the mitigation of both the translational and torsional responses of the asymmetric structure. Likewise, the effectiveness of a single ATMD with the optimum positions is presented and compared with that of the AMTMD.

Control strategy of the lever-type active multiple tuned mass dampers for structures

Li, Chunxiang,Han, Bingkang Techno-Press 2007 Wind and Structures, An International Journal (WAS Vol.10 No.4

The lever-type active multiple tuned mass dampers (LT-AMTMD), consisting of several lever-type active tuned mass dampers (LT-ATMD), is proposed in this paper to attenuate the vibrations of long-span bridges under the excitation directly acting on the structure, rather than through the base. With resorting to the derived analytical-expressions for the dynamic magnification factors of the LT-AMTMD structure system, the performance assessment then is conducted on the LT-AMTMD with the identical stiffness and damping coefficient but unequal mass. Numerical results indicate that the LT-AMTMD with the actuator set at the mass block can provide better effectiveness in reducing the vibrations of long-span bridges compared to the LT-AMTMD with the actuator set at other locations. An appealing feature of the LT-AMTMD with the actuator set at the mass block is that the static stretching of the spring may be freely adjusted in accordance with the practical requirements through changing the location of the support within the viable range while maintaining the same performance (including the same stroke displacement). Likewise, it is shown that the LT-AMTMD with the actuator set at the mass block can further ameliorate the performance of the lever-type multiple tuned mass dampers (LT-MTMD) and has higher effectiveness than a single lever-type active tuned mass damper (LT-ATMD). Therefore, the LT-AMTMD with the actuator set at the mass block may be a better means of suppressing the vibrations of long-span bridges with the consequence of not requiring the large static stretching of the spring and possessing a desirable robustness.

Control strategy of the lever-type active multiple tuned mass dampers for structures

Chunxiang Li,Bingkang Han 한국풍공학회 2007 Wind and Structures, An International Journal (WAS Vol.10 No.4

The lever-type active multiple tuned mass dampers (LT-AMTMD), consisting of several lever-type active tuned mass dampers (LT-ATMD), is proposed in this paper to attenuate the vibrations of long-span bridges under the excitation directly acting on the structure, rather than through the base. With resorting to the derived analytical-expressions for the dynamic magnification factors of the LT-AMTMD structure system, the performance assessment then is conducted on the LT-AMTMD with the identical stiffness and damping coefficient but unequal mass. Numerical results indicate that the LT-AMTMD with the actuator set at the mass block can provide better effectiveness in reducing the vibrations of long-span bridges compared to the LT-AMTMD with the actuator set at other locations. An appealing feature of the LT-AMTMD with the actuator set at the mass block is that the static stretching of the spring may be freely adjusted in accordance with the practical requirements through changing the location of the support within the viable range while maintaining the same performance (including the same stroke displacement). Likewise, it is shown that the LT-AMTMD with the actuator set at the mass block can further ameliorate the performance of the lever-type multiple tuned mass dampers (LT-MTMD) and has higher effectiveness than a single lever-type active tuned mass damper (LT-ATMD). Therefore, the LT-AMTMD with the actuator set at the mass block may be a better means of suppressing the vibrations of long-span bridges with the consequence of not requiring the large static stretching of the spring and possessing a desirable robustness.

Estimation of active multiple tuned mass dampers for asymmetric structures

Chunxiang Li,Xueyu Xiong 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.5

This paper proposes the application of active multiple tuned mass dampers (AMTMD) for translational and torsional response control of a simplified two-degree-of-freedom (2DOF) structure, able to represent the dynamic characteristics of general asymmetric structures, under the ground acceleration. This 2DOF structure is a generalized 2DOF system of an asymmetric structure with predominant translational and torsional responses under earthquake excitations using the mode reduced-order method. Depending on the ratio of the torsional to the translational eigenfrequency, i.e. the torsional to translational frequency ratio (TTFR), of asymmetric structures, the following three cases can be distinguished: (1) torsionally flexible structures (TTFR < 1.0), (2) torsionally intermediate stiff structures (TTFR = 1.0), and (3) torsionally stiff structures (TTFR > 1.0). The even distribution of the AMTMD within the whole width and half width of the asymmetric structure, thus leading to three cases of installing the AMTMD (referred to as the AMTMD of case 1, AMTMD of case 2, AMTMD of case 3, respectively), is taken into account. In the present study, the criterion for searching the optimum parameters of the AMTMD is defined as the minimization of the minimum values of the maximum translational and torsional displacement dynamic magnification factors (DMF) of an asymmetric structure with the AMTMD. The criterion used for assessing the effectiveness of the AMTMD is selected as the ratio of the minimization of the minimum values of the maximum translational and torsional displacement DMF of the asymmetric structure with the AMTMD to the maximum translational and torsional displacement DMF of the asymmetric structure without the AMTMD. By resorting to these two criteria, a careful examination of the effects of the normalized eccentricity ratio (NER) on the effectiveness and robustness of the AMTMD are carried out in the mitigation of both the translational and torsional responses of the asymmetric structure. Likewise, the effectiveness of a single ATMD with the optimum positions is presented and compared with that of the AMTMD.

A framework for fast estimation of structural seismic responses using ensemble machine learning model

Chunxiang Li,Hai Li,Xu Chen 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.28 No.3

While recognized as most rigorous procedure leading to 'exact' structural seismic responses, nonlinear time history analysis is usually time consuming and computational demanding, especially when numerous structures remain to be analyzed. This paper proposes a framework to improve the time efficiency in evaluating the structural seismic demands, using ensemble machine learning models based on 'classification-regression' philosophy. Typical tall pier bridges widely located in southwest China are employed as illustrative examples to validate the efficiency and performance of this proposed framework. The results and discussion show that with properly selected input variables, the proposed ensemble model (ORF-ANN herein) performs better in predicting seismic demands than other single learning algorithms (i.e., ANN and ORF), while the time efficiency is improved over 90%. This proposed model could drastically improve the efficiency for determining structural parameters in preliminary design process, and thus reduce the iterations of trail analysis. Additionally, the model constructed from proposed framework is believed especially favored for evaluating the post-earthquake states/resilience of a region and/or highway network, where thousands of structures might be contained, and conducting nonlinear time history analysis for each one would be prohibitively time consuming and delay the rescue operations.

Combined Application Effects of Arbuscular Mycorrhizal Fungi and Biochar on the Rhizosphere Fungal Community of Allium fistulosum L.

Ji Chunxiang,Li Yingyue,Xiao Qingchen,Li Zishan,Wang Boyan,Geng Xiaowan,Lin Keqing,Zhang Qing,Jin Yuan,Zhai Yuqian,Li Xiaoyu,Chen Jin 한국미생물·생명공학회 2023 Journal of microbiology and biotechnology Vol.33 No.8

Arbuscular mycorrhizal fungi (AMF) are widespread soil endophytic fungi, forming mutualistic relationships with the vast majority of land plants. Biochar (BC) has been reported to improve soil fertility and promote plant growth. However, limited studies are available concerning the combined effects of AMF and BC on soil community structure and plant growth. In this work, a pot experiment was designed to investigate the effects of AMF and BC on the rhizosphere microbial community of Allium fistulosum L. Using Illumina high-throughput sequencing, we showed that inoculation of AMF and BC had a significant impact on soil microbial community composition, diversity, and versatility. Increases were observed in both plant growth (the plant height by 8.6%, shoot fresh weight by 12.1%) and root morphological traits (average diameter by 20.5%). The phylogenetic tree also showed differences in the fungal community composition in A. fistulosum. In addition, Linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed that 16 biomarkers were detected in the control (CK) and AMF treatment, while only 3 were detected in the AMF + BC treatment. Molecular ecological network analysis showed that the AMF + BC treatment group had a more complex network of fungal communities, as evidenced by higher average connectivity. The functional composition spectrum showed significant differences in the functional distribution of soil microbial communities among different fungal genera. The structural equation model (SEM) confirmed that AMF could improve the microbial multifunctionality by regulating the rhizosphere fungal diversity and soil properties. Our findings provide new information on the effects of AMF and biochar on plants and soil microbial communities.

Delayed Deproteinization Causes Methodological Errors in Amino Acid Levels in Plasma Stored at Room Temperature or -20℃

Li, Junyou,Piao, Chunxiang,Jin, Huazi,Wongpanit, Kannika,Manabe, Noboru Asian Australasian Association of Animal Productio 2009 Animal Bioscience Vol.22 No.12

Deproteinization has been recognized as a prerequisite for amino acid analysis of plasma samples. For plasma stored at room temperature, delaying deproteinization for 30, 60 or 120 minutes did not result in significant changes in the mean CV (coefficient of variation), which ranged from 4.4 to 5.6%. However the mean CV of aspartic acid, ${\alpha}$-aminoadipic acid, alanine and lysine was about 10%. When the plasma was stored frozen at -20${^{\circ}C}$, the CV was increased at 0 and 120 minutes after thawing, to 12.4% (range, 4.1 to 35.3%) and 8.0% (2.5 to 30.7%), respectively. The concentrations in plasma during storage at room temperature of all the amino acids analyzed showed significant changes. In plasma stored for 30 minutes at room temperature, 17 amino acids increased in concentrations and two decreased. Extending this period to 60 or 120 minutes increased the instability as compare to the reference group. Storing plasma at -20${^{\circ}C}$ for 2 weeks resulted in significantly greater changes in the amino acid concentrations than at room temperature. On extending the storage time at room temperature, after thawing, to 30, 60, and 120 minutes, 21, 20, and all 22 amino acids respectively changed significantly (p<0.01). The present study indicates that methodological errors occur in the concentrations determined for all amino acids when plasma is left at room temperature. The storage of frozen non-deproteinized plasma accompanied more significant changes in most amino acid concentrations and thus should be avoided. Deproteinization should be performed as soon as possible after plasma collection.

Fabrication of the Ti5Si3/Ti Composite Inoculants and Its Refining Mechanism on Pure Titanium

Nuo Li,Chunxiang Cui,Shaungjin Liu,Long Zhao,Shuiqing Liu 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.2

The in situ Ti5Si3/Ti inoculants were successfully prepared by vacuum arc-melting and melt-spinning method. An efficient route by adding a small quantity of Ti5Si3/Ti inoculants to Ti melt has been first proposed tomodify the coarse grains of as cast microstructure of pure titanium in this paper. It was found that themicrostructure of ribbon inoculants was cellular structure that composed of Ti5Si3 and α-Ti phases. Thegrain refining effect of the inoculants was significantly improved with the adding ratio range from 0.2% to0.5% in weight. With the increase of addition amount of inoculants on Ti melt, the tensile strength, yieldstrength and microhardness of pure titanium are significantly improved except elongation. The excellentgrain refining effect can be attributed to the heterogeneous nucleation of the titanium grain on the precipitatedTi5Si3 phases in the Si-rich regions and the constitutional supercooling of Si in the Si-poverty regions. It issuggested that the in situ Ti5Si3/Ti inoculants is a promising inoculants for titanium alloys.

Performance of multiple tuned mass dampers-inerters for structures under harmonic ground acceleration

Liyuan Cao,Chunxiang Li,Xu Chen 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.1

This paper proposes a novel high performance vibration control device, multiple tuned mass dampers-inerters(MTMDI), to suppress the oscillatory motions of structures. The MTMDI, similar to the MTMD, involves multiple tuned mass damper-inerter (TMDI) units. In order to reveal the basic performance of the MTMDI, it is installed on a single degree-of-freedom (SDOF) structure excited by the ground acceleration, and the dynamic magnification factors (DMF) of the structure-MTMDI system are formulated. The optimization criterion is determined as the minimization of maximum values of the relative displacement's DMF for the controlled structure. Based on the particle swarm optimization (PSO) algorithm to tune the optimum parameters of the MTMDI, its performance has been investigated and evaluated in terms of control effectiveness, strokes, stiffness and damping coefficient, inerter element force, and robustness in frequency domain. Meanwhile, further comparison between the MTMDI with MTMD has been conducted. Numerical results clearly demonstrate the MTMDI outperforms the MTMD in control effectiveness and strokes of mass blocks. Additionally, in the aspects of frequency perturbations on both earthquake excitations and structures, the robustness of the MTMDI is also better than the MTMD.

중국 조선족 청소년들의 자아정체성 및 사회정체성과 학교적응의 관계

성춘향 ( Cheng Chunxiang ),이예화 ( Li Yihua ),박용환 ( Park Yonghan ) 충남대학교 교육연구소 2017 교육연구논총 Vol.38 No.2

본 연구에서는 중국 조선족 청소년들의 자아정체성 및 사회정체성과 학교적응간의 관계에 대해 알아보고자 하였다. 특히 최근 다문화와 세계시민성과 같은 개념이 대두되면서 사회정체성의 역할이 강조되고 있는데, 이와 관련하여 한국의 청소년들과는 다른 독특한 사회적 환경에서 살아가고 있는 조선족 청소년들의 사회정체성에 주목하고자 하였다. 이를 위해 중국 연변조선족자치주 연길시의 모 중학교 1,2학년에 재학 중인 남여 조선족 중학생 192명(남 80명, 여 112명)을 대상으로 설문을 실시하였다. 주요 연구결과는 다음과 같다. 첫째, 조선족 중학생들의 자아정체성과 사회정체성은 이들의 학교적응 및 그 하위요인을 유의미하게 예측해주는 것으로 나타났다. 둘째, 조선족 중학생들의 자아정체성을 통제한 상태에서 사회정체성은 학교적응에 대해 고유설명력을 보였는데 이는 조선족 중학생들의 사회정체성이 학교적응을 설명하는데 있어서 독립적으로 기여하는 부분이 있다는 것을 의미한다. 이러한 연구결과는 오늘날 복잡한 사회적 환경에서 살아가고 있는 청소년들이 학교생활에 적응함에 있어 자아정체성뿐만 아니라 사회정체성 역시 하나의 주요한 요인으로 작용하고 있음을 시사한다. This study explored the relations of self identity and social identity to school adjustment for Korean-Chinese adolescents. Lately, the role of social identity has been emphasized as the concepts such as multi-culturalism and global citizenship emerge. In this regard, we were more interested in the social identity of Korean-Chinese adolescents who live in a unique social environment. For these proposes, we administered a survey of two types of identity and school adjustment to 192 Korean-Chinese middle-school students (males 80, females 112) in first and second grades of middle-schools in Yanji, China. The main results are as follows. First, the self identity of Korean-Chinese middle-school students significantly predicted their school adjustment. Second, social identity also predicted school adjustment significantly, even after the effect of self identity was controlled for. The results indicate that not only self identity but also social identity may affect adolescents` school adjustment especially for those living in a complex social contexts.