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Monitoring the Modal Frequency and velocity variations of Bridges under Ambient Excitation

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Earthquake Research in China 2015年第4期29卷 554-566页

作者： Chen Haichao Ge Hongkui Meng Fanbao Wang Xiaoqiong Yang Wei Unconventional Natural Gas Institute China University of Petroleum-Beijing Institute of Geophysics China Earthquake Administration

We conducted a long-term monitoring experiment on the Lutuanxilu Bridge located in Changping District of Beijing, employing our recently developed real-time bridge monitoring system based on the Guralp CMG-6TD broadband seismometer. We identified the modal parameters with the stochastic subspace identification( SSI) algorithm,and continuously monitored the temporal velocity variation with coda wave *** results show that:( 1) the highly sensitive Guralp CMG-6TD broadband seismometer,which records the three-component vibration signal within broad frequency range,is well suited for long-term bridge health monitoring.( 2) With the continuous vibration signal from ambient excitation,the stochastic subspace algorithm can robustly identify the low-order modal parameters and the coda wave interferometry can accurately monitor the tiny velocity variation.( 3) The elastic modulus of bridge materials changes significantly associated with varying temperature,leading to diurnal velocity variation with amplitude of approximately 1%. The velocity variation shows strong negative correlation with temperature fluctuation. Meanwhile,the modal frequencies remain quite stable,suggesting that the velocity variation may be a more sensitive quantitative damage index.( 4) While the modal frequencies reflect the integrated health status of the bridge,the velocity variation can be utilized to monitor the local elastic modulus. Therefore,it is crucial for bridge health monitoring to continuously monitor the two key damage indexes under ambient excitation.

关键词： Ambient excitation Stochastic subspace Identification Coda wave interferometry Modal frequency velocity variation

Behavior of Shock Waves Formed by Unsteady Supersonic Jet Injected into Cell

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Journal of Thermal Science 2008年第1期17卷 50-55页

作者： Minoru YAGA Hiroshi FUKUOKA Yasushi IWATA Toshio TAKIYA Depts.Mech.Systems Eng. Univ.of the RyukyusSenbaru 1NishiharaOkinawa903-0213 Professor Graduate student Faculty of Eng.Univ.of the RyukyusSenbaru 1NishiharaOkinawa903-0213 Nanoelectronics Research Institute AIST Tsukuba Central 2Tsukuba 305-8568 Hitachi Zosen Corporation 2-11 Funamachi2 chomeTaishou-kuOsaka 551-0022

The unsteady behavior of flow driven by a jet suddenly injected into a cell is numerically studied by solving the axisymmelric two-dimensional compressible Navier-Stokes equations. The system of the calculation is a model of the laser ablation of a certain duration followed by a discharging process through the exit hole at the down- stream end of the cell. In the calculations, the contour of the cell is changed while other parameters such as the Mach number of the jet, its duration, and the diameter of the cell exit are fixed. Monitoring the velocity at the exit hole is used to investigate the influence of the shape on the interaction between the shock wave and the jet. As the result, it was found that the velocity peak value and its arrival time at the downstream end of the cell exit are determined by the diameter of the cell.

关键词： Shock wave CFD supersonic flow unsteady jet velocity variation

Entry and Exit Stress variation of Cold Rolling Strip

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Journal of Iron and Steel Research International 2012年第6期19卷 19-24页

作者： WANGDong—cheng StateKeyLaboratoryofMetastableMaterialsScienceandTechnology NationalEngineeringResearchCenterforEquipmentandTechnologyofColdRollingStripYanshanUniversityQinhuangdao066004HebeiChina

The shortcomings of an exit stress variation formula which has been well accepted are analyzed~ it is found that the exit stress variation formula violates the premise of the law of volume constancy. The shortcomings of an en- try stress variation formula are analyzed too, and the basic assumption of the formula is uniform exit velocity. How- ever, for a rigid-plastic material uniform exit velocity implies that the lateral distributioi1 of elongation is uniform, so the exit stress must be uniform and any type of flatness defect is impossible, which is contrary to the practice. In fact, entry and exit velocity variation influence entry and exit stress variation, and entry and exit stress variation in- fluence entry and exit velocity variation too, so a precise explicit stress variation formula cannot be got easily. Con- sidering the relationship between stress variation and velocity variation, an iteration method is presented to calculate entry and exit stress variation of cold rolling strip. To avoid divergent phenomenon of the iteration course, a relaxa- tion factor method is adopted. The calculation results are compared with the entry and exit stress variation formula commonly used by many researchers. The difference is remarkable, while the result calculated agree more well with measured result if the exit elastic recovery zone is considered. Specially, the incoming flatnessI propagate efficiency calculated ~ives a more realistic result.

关键词： cold rolling stress variation velocity variation iteration method relaxation factor method