Identification and characterization of galloping of Tsuruga test line based on multi-channel modal analysis of field data

In spite of several signal processing and system identification techniques, discussion on field-observed galloping of overhead transmission lines is still based on primitive form of field data such as time series, Lissajous diagrams and power spectra. Any form of large amplitude vibration in ice storms is defined as galloping and an attempt has seldom made in identifying whether such vibrations are self-excited modal responses. In doing so, there are always possibilities of misinterpreting gust response as galloping. In this study, a method of multi-channel modal analysis consisting of random decrement method (RDM) and eigensystem realization algorithm (ERA) is proposed to identify galloping, which is self-excited modal response based on a typical field-monitored data of wind-induced vibration of the Tsuruga Test line. RDM was used to transform the field data into non-forced response component, which is similar to free vibration response, and ERA was used to extract modal parameters from the non-forced components. Based on these modal parameters, galloping events were identified, and characteristics of galloping such as coupled translational and rotational motions, and nature of full span vibration, oscillation envelopes and influence of geometry of the line section to its occurrence are discussed. Result of analysis has confirmed well-known mechanism of bundle conductor galloping, which is galloping of bundle transmission lines involves significant coupling of vertical and torsional motions. As for the characteristics of bundle conductor galloping, the most likely galloping mode in deadend span is found as first asymmetric mode and large amplitude of galloping occurs when torsion is in-phase with vertical velocity. Furthermore, it is found that deadend span line section is more prone to galloping than semi-suspension span line section. Finally, performance of proposed method was tested by introducing usual buffeting analysis, and it is confirmed that it has immense potential to identify and characterize galloping based on field data.textapplication/pdfjournal articl

Control of cable vibrations using secondary cable with special reference to nonlinearity and interaction

http://www.sciencedirect.com/science/journal/09215093 | http://www.sciencedirect.com/science/journal/09215093Experimental as well as analytical studies have been carried out on the controlling effects of a secondary cable in a cable system and efforts have been made to explain the results, especially on the basis of nonlinearity in response and interaction. A cable model consisting of two identical sagged cables in parallel connected by another lighter secondary cable was selected for investigations. Experimental results reveal that nonlinearity in the secondary cable motion induces the main cables to vibrate with nonlinear motion consisting of sub-harmonic components in response in addition to a simple harmonic component. Analytical investigations based on the solution of nonlinear equations of motion, derived from a modal synthesis approach with substructural formulations, show an early jump in the frequency response curve of the main cable. Generation of closely spaced modes due to the addition of the secondary cable plays an important role on its controlling effects on the main cable response through this type of nonlinear interaction.textapplication/pdfjournal articl

Dynamic characteristics and vibration control of a cable system with substructural interactions

http://www.sciencedirect.com/science/journal/09215093 | http://www.sciencedirect.com/science/journal/09215093Free and forced vibration analyses of a cable system, which consists of two identical sagged cables in parallel connected by another sagged cross cable, are conducted using a modal synthesis method with substructural formulation. The analyses are carried out in order to investigate the system behavior, while paying attention to the substructural interaction. It is shown that the secondary cable contribution in the system modal damping can be dominant and can cause greater damping in the case of coupled motion of main and secondary cables. The importance of the secondary cable in transferring the energy from one substructure to another through the substructural interaction is also discussed for the passive control of harmonically forced vibration in the main cable.textapplication/pdfjournal articl

構造健全度評価のための常時微動計測とモード・減衰変化同定の精緻化 : 富州原橋（ローゼ橋）を例として

3 若手研究及び基礎研究textapplication/pdfresearch repor

科学分析支援センターの設立30周年にして初めて・・・《巻頭言》

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科学分析支援センターのミッション《巻頭言》

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構造物の常時微動計測と減衰変化同定の精緻化に基づく健全度評価

４ 若手研究及び基礎研究textapplication/pdfresearch repor

ミッションの再定義に基づく研究力と人材育成の強化《巻頭言》

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Identification of large amplitude wind-induced vibration of ice-accreted transmission lines based on field observed data

http://www.sciencedirect.com/science/journal/01410296 | http://www.sciencedirect.com/science/journal/01410296This study presents a method to identify the periodic galloping response and random gust response of transmission line based on field observed data and to separate major galloping component from mix mode of gust and galloping vibration. Time-averaged characteristics of wind-induced vibration are discussed based on spectral analysis and non-stationary characteristics are considered to identify the wind-induced vibration quantitatively by applying Prony’s method in piecewise fashion. By applying highpass filter major galloping response component is separated from mixed response and characteristics of thus separated major galloping response component are compared with those of total response. Results of these analyses show possibilities of large amplitude galloping as well as gust response in in-plane vertical motion in ice-accreted transmission line. Applicability of random decrement method to estimate the existence of periodic correlated galloping component is also discussed.textapplication/pdfjournal articl

モジュラー型エキスパンションジョイントの騒音発生源の究明とその騒音防止対策の研究

This study investigates the mechanism of noise generation from the modular type joint and to quantify the effectiveness of countermeasures. The field measured data was first analyzed and a series of experiments was then conducted with a full scale model of the modular type joint, where the noise and vibration characteristics of the joint with and without countermeasures were investigated under a vehicle passage. The dynamic characteristics of the joint and the acoustical characteristics of the gap of the joint were also examined.textapplication/pdfdepartmental bulletin pape