• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.152-157
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• 2018

The degradation and damage of the components for ballasted track could be caused a serious problem for railway safety. Therefore, the integrity evaluation of ballasted track condition is important to ensure and predict that the track safety and track maintenance. Various track components such as rail pad, ballast, sleeper, and rail that are widely used in Republic of Korea and represent a range of physical properties have been selected for this research. In this study, the experimental modal analysis was performed by the non-destructive testing. Modal test results were obtained from the field test and used to assess the condition of the track components. From the field test, the system of ballasted track was found to be simplified as a two-degree-of-freedom(2DOF) dynamic system. The condition of track component was found to directly affect the dynamic response of ballasted tracks. As the results, the dynamic properties of the track component was depend on the track condition and was distributed more roughly and over a wider range than its initial design values. Further, the methodology presented in this study is possible to determine experimentally the fundamental track parameters which are required in the numerical analysis, and also are useful for the safety assessment of track condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.629-634
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• 2004

Modal parameters of the total missile structure including a hinge mechanism are estimated by the experimental modal analysis. The free-free boundary condition is simulated by hanging the missile structure with a wire rope, and the missile structure is excited by the random vibration technique. Test results are used to verify the FE analysis, the 1-D FE model is modified by 3-D model at the hinge part. Consequently, the modal parameters of the missile structure are estimated preciously.

• Structural Monitoring and Maintenance
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• v.10 no.3
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• pp.191-205
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• 2023

In this paper, through operational modal analysis and ambient vibration tests, the dynamic characteristics of a multi-span simply-supported reinforced concrete highway bridge deck was determined and the results were used to assess the quality of construction of the individual spans. Supporting finite element (FE) models were created and analyzed according to the design drawings. After carrying out the dynamic tests and extracting the modal properties of the deck, the quality of construction was relatively assessed by comparing the results obtained from all the tests from the individual spans and the FE results. A comparison of the test results among the different spans showed a maximum difference value of around 9.3 percent between the superstructure's natural frequencies. These minor differences besides the obtained values of modal damping ratios, in which the differences were not more than 5 percent, can be resulted from suitable performance, health, and acceptable construction quality of the bridge.

• Smart Structures and Systems
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• v.15 no.3
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• pp.717-733
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• 2015

Modal parameters of a structure are commonly used quantities for system identification and damage detection. With a limited number of studies on the statistics assessment of modal parameters, this paper presents procedures to properly account for the uncertainties present in the process of extracting modal parameters. Particularly, this paper focuses on how to deal with the measurement error in an ambient vibration test and the modeling error resulting from a modal parameter extraction process. A bootstrap approach is adopted, when an ensemble of a limited number of noised time-history response recordings is available. To estimate the modeling error associated with the extraction process, a model prediction expansion approach is adopted where the modeling error is considered as an "adjustment" to the prediction obtained from the extraction process. The proposed procedures can be further incorporated into the probabilistic analysis of applications where the modal parameters are used. This study considers the effects of the measurement and modeling errors and can provide guidance in allocating resources to improve the estimation accuracy of the modal data. As an illustration, the proposed procedures are applied to extract the modal data of a damaged beam, and the extracted modal data are used to detect potential damage locations using a damage detection method. It is shown that the variability in the modal parameters can be considered to be quite low due to the measurement and modeling errors; however, this low variability has a significant impact on the damage detection results for the studied beam.

• Smart Structures and Systems
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• v.17 no.3
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• pp.491-522
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• 2016

A benchmark problem for modal identification of a cable-stayed bridge was proposed by a research team at Hong Kong Polytechnic University. By taking an instrumented cable-stayed bridge as a test bed, nineteen sets of vibration records with known/unknown excitations were provided to invited researchers. In this paper, the vibration responses of the bridge under a series of excitation conditions are examined to estimate the wind and traffic-induced variations of its dynamic characteristics. Firstly, two output-only experimental modal identification methods are selected. Secondly, the bridge and its monitoring system are described and the nineteen sets of vibration records are analyzed in time-domain and frequency-domain. Excitations sources of blind datasets are predicted based on the analysis of excitation conditions of known datasets. Thirdly, modal parameters are extracted by using the two selected output-only modal identification methods. The identified modal parameters are examined with respect to at least two different conditions such as traffic- and typhoon-induced loadings. Finally, the typhoon-induced effects on dynamic characteristics of the bridge are estimated by analyzing the relationship between the wind velocity and the modal parameters.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.98-101
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• 2006

As an alternative of conventional prestressed concrete (PSC) girders, various types of PSC girders are being developed and applied in bridge structures. Incrementally prestressed concrete girder is one of these newly developed girders. According to design concept, these new types of PSC girders have considerable advantages to reduce their self-weight and make spans longer. However, dynamic interaction between bridge superstructures and passing trains would be sometimes one of critical issues in these more flexible railway bridges. Therefore, it is very important to evaluate modal parameters of newly designed bridges before conducting dynamic analyses. In the present paper, a 25 meters long full scale PSC girder was fabricated as a test specimen and modal testing was carried out to evaluate modal parameters including natural frequencies and modal damping ratios at every prestressing stage. In the modal testing, a digitally controlled vibration exciter as well as an impact hammer is applied to obtain frequency response functions more exactly and the modal parameters are evaluated varying with construction stages. Prestressed force effects on changes of modal parameters are analyzed at every incremental prestressing stage.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.13 no.2
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• pp.151-154
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• 2002

Background and Objectives : The pitch range of the human voice is variable, extending from chest register to falsetto register. Although numerous studies have investigated after laryngeal mechanism description of falsetto tone, systematic and objective studies were lack. The purpose of this study was to systematically analyze and compare modal with falsetto voice. Materials and Methods : Seven adult baritones were selected from a larger population of volunteers at choir. Simultaneous measurements of acoustic, electroglottographic and aerodynamic study were made during /e/ sustained in two vocal registers, lowest modal and highest falsetto. Statistical analysis was performed using Wilkoxson signed rankes test. Results : In the acoustic analysis, shimmer was increased in flasetto voice(p<0.05). In the electroglottographic analysis, closed quotient(CQ), speed quotient(SQ) at the modal voice were higher than at the falsetto voice(p<0.05). In the aerodynamic analysis, and airflow rate(MFR) of falsetto voice was higher than modal voice(p<0.05). Conclusions : In the results of the study indicate that, falsetto register ineffective, inefficient, generally unpleasant because it was produced by incomplete clousure of true vocal cord. We anticipated that further study with large samples can provide an objective criteria for status and classification of singer's modal and falsetto voice.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.308-314
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• 1999

This paper presents the results of structural identification of a safety-related valve for nuclear power plant by impact hammer test as well as shaking table tests by using broadband random wave and sine sweep excitation. The test specimen is a Y-type motor operated globe valve. The test was performed as a "support test" to validate the analytically obtained modal parameters of the valve during its seismic qualification process by analytical method. From the study results it has been found that the shaking table test generally yields higher natural frequencies and lower damping values compared with those of impact hammer test. And it has been recognized that impact hammer test for modal identification of complex structures should be applied very carefully to get reasonable results.e results.

• The Journal of the Korea Contents Association
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• v.19 no.11
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• pp.144-152
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• 2019

Learning styles are the methods of gathering, processing, interpreting, organizing the information. VARK learnig inventory is instructional preference classified according to their visual(V), aural(A), read-write(R), and/or kinesthetic(K) sensory modality preferences(SMP). Learner-centered learning is emphasized, but there are few studies on VARK learning styles in Korean medical school. The purposes of this study were to assess the student' SMPs and compare those with gender, status, and academic achievement. The subjects of study were 394 students at C Medical School and Graduate School of Medicine. For the study style test, 16 questions were used in Korean version of VARK test paper© 7.0 developed by Fleming provided on the VARK website. Academic achievement was converted into a standardized score(t score). Frequency analysis, cross analysis, and variance analysis(t-test, ANOVA) were conducted to identify learning style disposition and differences between groups. The uni-modal type was 87(22.1%) and the multimodal was 307(77.9%). Regardless of gender, quasi-modal VARK was the most preferred. There was no significant difference in learning styles by gender. The first grade in medicine was the lowest in uni-modal type(8.8%) and the highest in quasi-modal VARK type(47.8%), while the fourth grade was the highest in uni-modal type(30.7%) and the lowest in quasi-modal VARK type(19.8%) and tri-modal type(19.8%). There was no difference in academic achievement by all learning types(F=1.09, p=0.37). The knowledge about students' learning styles is helpful for instructors to apply more learner-centered teaching strategies in medical education.

• Journal of Korea Multimedia Society
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• v.8 no.8
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• pp.1119-1133
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• 2005

As a very important part in development of the protocol, verification and conformance test for protocol specification are complementary techniques that are used to increase the level of confidence in the system functions as prescribed by their specifications. In this paper, we verify the safety and liveness properties of rail signal control protocol type 1 specified in LTS with model checking method, and experimentally prove that it is possible to check for the deadlock, livelock and rechability of the states and actions on LTS. The implemented formal checker is able to verify whether properties expressed in modal logic are true in specifications using modal mu-calculus. We also propose a formal method on generation of conformance test cases using the concept of UIO sequences from verified protocol specification. The suggested tools are implemented by C++ language under Windows NT.