• Earthquakes and Structures
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• v.8 no.4
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• pp.859-887
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• 2015

Structural health monitoring (SHM) has gained in popularity in recent years since it can assess the performance and condition of instrumented structures in real time and provide valuable information to the asset's manager and owner. Operational modal analysis plays an important role in SHM and it involves the determination of natural frequencies, damping ratios and mode shapes of a constructed structure based on measured dynamic data. This paper presents the operational modal analysis and seismic response characterization of the Tsing Ma Suspension Bridge of 2,160 m long subjected to different earthquake events. Three kinds of events, i.e., short-distance, middle-distance and long-distance earthquakes are taken into account. A fast Bayesian modal identification method is used to carry out the operational modal analysis. The modal properties of the bridge are identified and compared by use of the field monitoring data acquired before and after the earthquake for each type of the events. Research emphasis is given on identifying the predominant modes of the seismic responses in the deck during short-distance, middle-distance and long-distance earthquakes, respectively, and characterizing the response pattern of various structural portions (deck, towers, main cables, etc.) under different types of earthquakes. Since the bridge is over 2,000 m long, the seismic wave would arrive at the tower/anchorage basements of the two side spans at different time instants. The behaviors of structural dynamic responses on the Tsing Yi side span and on the Ma Wan side span under each type of the earthquake events are compared. The results obtained from this study would be beneficial to the seismic design of future long-span bridges to be built around Hong Kong (e.g., the Hong Kong-Zhuhai-Macau Bridge).

• Steel and Composite Structures
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• v.28 no.2
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• pp.223-231
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• 2018

Nowadays, there are a great number of various structures that have been retrofitted by using different FRP Composites. Due to this, more researches need to be conducted to know more the characteristics of these structures, not only that but also a comparison among them before and after the retrofitting is needed. In this research, a model steel structure is tested using a bench-scale earthquake simulator on the shake table, using recorded micro tremor data, in order to get the dynamic behaviors. Columns of the model steel structure are then retrofitted by using GFRP composite, and then tested on the Quanser shake table by using the recorded micro tremor data. At this stage, it is needed to evaluate the dynamic behaviors of the retrofitted model steel structure. Various types of methods of OMA, such as EFDD, SSI, etc. are used to take action in the ambient responses. Having a purpose to learn more about the effects of GFRP composite, experimental model analysis of both types (retrofitted and no-retrofitted models) is conducted to evaluate their dynamic behaviors. There is a provision of ambient excitation to the shake table by using recorded micro tremor ambient vibration data on ground level. Furthermore, the Enhanced Frequency Domain Decomposition is used through output-only modal identification. At the end of this study, moderate correlation is obtained between mode shapes, periods and damping ratios. The aim of this research is to show and determine the effects of GFRP Composite implementation on structural responses of the model steel structure, in terms of changing its dynamical behaviors. The frequencies for model steel structure and the retrofitted model steel structure are shown to be 33.916% in average difference. Finally, it is shown that, in order to evaluate the period and rigidity of retrofitted structures, OMA might be used.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.99-105
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• 2010

The concentration and size analysis of in-situ suspended particulate material were measured using an optical instrument, LISST-100, in the bottom layer at the three inlets of the Seomjin River Estuary, mouth of Gwangyang bay, and Gwangyang bay-side of the Namhae Bridge. In the Seomjin river estuary and mouth of Gwangyang bay-side of the Namhae Bridge, the in-situ mean grain size of the suspended material changed from a uni-modal distribution with a dominant peak at a coarse fraction to a bi-modal distribution with a secondary peak at the finer particles. Seomjin River. The interactions between suspended particulate concentration and beam attenuation coefficient of suspended particulate matters depended on the supply of finer and coarser particles in the mouth of Gwangyang Bay and Seomjin River. So, interactions reflected difference of the concentration, mean size and sorting of suspended particulate matters. The difference of interaction showed dynamic behaviors to the resuspension and deflocculation processes increased river discharge. This showed that it may be possible to use the interactions between the suspended particle concentration and beam attenuation coefficient to monitor the temporal and spatial distributions of in-situ particles.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.3 no.4
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• pp.344-365
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• 2009

The performance of a tracking system is greatly increased if multiple types of sensors are combined to achieve the objective of the tracking instead of relying on single type of sensor. To conduct the multi-modal tracking, we have previously developed a multi-modal sensor-based tracking model where acoustic sensors mainly track the objects and visual sensors compensate the tracking errors [1]. In this paper, we find a network synchronization problem appearing in the developed tracking system. The problem is caused by the different location and traffic characteristics of multi-modal sensors and non-synchronized arrival of the captured sensor data at a processing server. To effectively deliver the sensor data, we propose a time-based packet aggregation algorithm where the acoustic sensor data are aggregated based on the sampling time and sent to the server. The delivered acoustic sensor data is then compensated by visual images to correct the tracking errors and such a compensation process improves the tracking accuracy in ideal case. However, in real situations, the tracking improvement from visual compensation can be severely degraded due to the aforementioned network synchronization problem, the impact of which is analyzed by simulations in this paper. To resolve the network synchronization problem, we differentiate the service level of sensor traffic based on Weight Round Robin (WRR) scheduling at the routers. The weighting factor allocated to each queue is calculated by a proposed Delay-based Weight Allocation (DWA) algorithm. From the simulations, we show the traffic differentiation model can mitigate the non-synchronization of sensor data. Finally, we analyze expected traffic behaviors of the tracking system in terms of acoustic sampling interval and visual image size.

• Smart Structures and Systems
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• v.11 no.5
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• pp.533-553
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• 2013

In this paper, system identification of a cable-stayed bridge in Korea, the Hwamyung Bridge, is performed using vibration responses measured by a wireless sensor system. First, an acceleration based-wireless sensor system is employed for the structural health monitoring of the bridge, and wireless sensor nodes are deployed on a deck, a pylon and several selected cables. Second, modal parameters of the bridge are obtained both from measured vibration responses and finite element (FE) analysis. Frequency domain decomposition and stochastic subspace identification methods are used to obtain the modal parameters from the measured vibration responses. The FE model of the bridge is established using commercial FE software package. Third, structural properties of the bridge are updated using a modal sensitivity-based method. The updating work improves the accuracy of the FE model so that structural behaviors of the bridge can be represented better using the updated FE model. Finally, cable forces of the selected cables are also identified and compared with both design and lift-off test values.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.10
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• pp.113-120
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• 2006

A cam profile CNC grinding machine is developed for manufacture of high precision contoured cams. The developed machine is composed of the high precision spindle using boll bearings, the high stiffness box layer type bed and the three axis CNC controller with the high resolution AC servo motor. In this paper, structural and modal analysis for the developed machine is carried out to check the design criteria of the machine. The analysis is carried out by FEM simulation using the commercial software, CATIA V5. The machine is modeled by placing proper shell and solid finite elements. And also, this paper presents the measurement system and experimental investigation on the modal analysis of a grinding machine. The weak part of the machine is found by the experimental evaluation. The results provide structure modification data for good dynamic behaviors. And safety of the machine was confirmed by the modal analysis of modified machine design. Finally, the cam profile grinding machine was successfully developed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.1
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• pp.49-54
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• 2010

An integrated machining center is developed for high precision and productivity manufacturing. The developed machine is composed of the high precision spindle using ball bearings, the high stiffness bed and the three axis CNC controller with the high resolution AC servo motor. In this paper, structural and modal analysis for the developed machine are carried out to check the design criteria of machine. The analysis is carried out by FEM simulation with using the commercial software, CATIA V5, ANSYS and ARMD. The simulation model of machine is made by shell and solid finite elements. This study also presents the measurement system on the modal analysis of an integrated machining center. The weak part of the machine is found by the analytical evaluation. The results provide with the structural modification data for good dynamic behaviors. And the safety of machine is confirmed by the modal analysis of modified machine design. As this study results can be trustworthy with the analysis of ANSYS and CATIA, integrated machining center can be successfully developed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.495-501
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• 2001

In this paper, a new technique which models the joints characteristics through reduction of DOFs of structures with joints using component mode synthesis (CMS) method is proposed. Bolt joints are modeled by mass-spring systems. Also generalized mass and stiffness matrices for this models are introduced. Because bolt joints have influence on eigenvalues of structures, exact eigenvalues from modal test are used. The results show that the behaviors of structures with bolt joints depend to a large extent on the translational DOFs and not on rotational DOFs of mass and stiffness matrices of bolts. Furthermore it is confirmed that lumped mass-spring systems as models of bolt joints are effective models considering the facts that joint characteristics converged to constant values in some iterations and eignevalues from proposed method are in good agreement with ones from modal test.

• Structural Engineering and Mechanics
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• v.13 no.4
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• pp.429-436
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• 2002

The current work presents an analysis algorithm for the modal analysis for the dynamic behaviors of offshore structures with concepts of mass perturbation influence term. The mass perturbation concept by using the term, presented in this paper offers an efficient solution procedure for dynamical response problems of offshore structures. The basis of the proposed method is the mass perturbation influence concepts associated with natural frequencies and mode shapes and mass properties of the given structure. The mathematical formulation of the mass perturbation influence method is described. New solution procedures for dynamics analysis are developed, followed by illustrative example problems, which deal with the effectiveness of the new solution procedures for the dynamic analysis of offshore structures. The solution procedures presented herein is compact and computationally simple.

• Journal of KSNVE
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• v.9 no.1
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• pp.49-59
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• 1999

The mechanism of Stewart platform has many advantages for kinematic analysis and control. Thus there have been many research about employing this mechanism in the new type of machine tool. Since the vibration caused during the manufacturing process has a severely adverse effect on the machining precision. it is very important to enhance the vibrational characteristics. However. it is not easy to use finite element model for the vibration analysis. That is because the vibration behaviors of the structure vary in a complicated manner according as the length of links varies. In this paper, a Stewart platform type of machine tool is modeled in finite element method and then updated by using the experimental modal data. Finally. the static and dynamic characteristics of the finite element model are predicted and then discussed.