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Search Results: 1 - 10 of 4906 matches for " Jong Won Kwark "
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Comparison of Measured and Dynamic Analysis Vertical Accelerations of High-Speed Railway Bridges Crossed by KTX Train  [PDF]
Hyejin Yoon, Won Jong Chin, Jeong-Rae Cho, Jae Yoon Kang, Jongwon Kwark
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.59091
Abstract:

Since high-speed railway bridges are subjected to cyclic loading by the continuous wheel loads traveling at high speed and regular spacing, their dynamic behavior is of extreme importance and has significant influence on the riding safety of the trains. To secure the riding safety of the trains, advanced railway countries have limited the vertical acceleration of the bridge slab below critical values at specific frequency domains. Since these limitations of the vertical acceleration constitute the most important factors in securing the dynamic safety of the bridges, these countries have opted for a conservative approach. However, the Korean specifications limit only the size of the peak acceleration without considering the frequency domain, which impede significantly rational evaluation of the high-speed railway bridges in Korea. In addition, the evaluation of the acceleration without consideration of the frequency domain is the cause of disagreement between the dynamic analysis and measurement results. This study conducts field monitoring and dynamic analysis on high-speed railway bridges to gather the acceleration signals and compare them. Significant difference in the size of the vertical acceleration was observed between the measured and dynamic analysis accelerations when discarding the frequency domain as done in the current specifications. The comparison of the accelerations considering only low frequencies below 30 Hz showed that the dynamic analysis reflected accurately the measured vertical acceleration.

Computation of Impact Factor of High-Speed Railway Bridge by KTX Train Riding Test  [PDF]
Hyejin Yoon, Won Jong Chin, Jae Yoon Kang, Jongwon Kwark, Eui-Seung Hwang
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.59090
Abstract:

The design live load of railway is divided into common railway and high-speed railway separately inKorea. Accordingly, the Korean design specification of railway specifies the impact factor for common railway and high-speed railway respectively. The impact factor for high-speed railway is based on Eurocode. Since the impact factor criteria inKoreawere established by adopting those of the Eurocode and without dedicated investigation relying on research results reflecting the domestic circumstances, thorough examination should be implemented on these criteria. Therefore the evaluation of impact factor based on field tests is required. Both dynamic and static vertical displacements are necessary to compute the impact factor. The dynamic response can be obtained from the measurement of deflection of the bridge slab crossed by the firstKoreahigh-speed train (KTX, Korea Train eXpress) running at high-speed. The main difficulties encountered are in obtaining static response because static response corresponds to the response of the bridge when the train remains immobile on the bridge or crosses the bridge at speed slower than5 km/hr. This study introduces the static response derived by applying the moving average method on the dynamic response signal. To that goal, field measurements was conducted under train speeds of5 km/hr and ranging from100 km/hr to300 km/hr on Yeonjae Bridge located in the trial section of the Gyeonbu High-Speed Railway Line before its opening. The validity of the application of the moving average method is verified from comparison of measured static response and derived static response by moving average method. Moreover, evaluation is conducted on the impact factor computed for a bridge crossed by the KTX train running at operational speed.

A Study on the Bond Strength between High Performance Concrete and Reinforcing Bar  [PDF]
Eun Suk Choi, Jung Woo Lee, Seong Jun Kim, Jong Won Kwark
Engineering (ENG) , 2015, DOI: 10.4236/eng.2015.77033
Abstract: As a preliminary study for the erection of floating structures using high performance concrete, this paper examines the bond characteristics between concrete and the reinforcing bar. Since the floating structure is constructed in aquatic environment, corrosion of the reinforcing steel is likely to develop more prematurely than in onshore structure in case of concrete cracking. A solution to this corrosion problem could use FRP rebar instead of steel reinforcement. To that goal, an experimental study is conducted on the concrete-FRP bond strength to verify if such FRP rebar develops performance comparable to the conventional steel rebar. A series of tests are performed considering the bond length of ordinary steel rebar and G-FRP rebar as test variable with respect to the strength of concrete, and the results are presented.
Load-Measuring Pot Bearing with Built-In Load Cell —Part II: Fatigue Performance and Experimental Temperature Correction  [PDF]
Jeong-Rae Cho, Young Jin Kim, Jong-Won Kwark, Sung Yong Park, Won Jong Chin, Byung-Suk Kim
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.511108
Abstract:

This paper presents the results of fatigue performance tests performed up to 10 million cycles on a load-measuring pot bearing with built-in load cell to verify its field applicability and proposes an empirical temperature correction formula. In Part I of this work, various measurement performances of the load-measuring pot bearing were evaluated through static and dynamic loading tests. Bridge bearings are subjected to the effect of fatigue caused by the repeated application of moving loads and exposed to harsh site conditions including cold and hot weathers differently to laboratory conditions. Accordingly, the durability of the load-measuring pot bearing with built-in load cell shall be secured and the environmental effects like temperature shall be minimized for its application on field. This study conducted fatigue tests up to 10 million cycles on a load-measuring pot bearing with the capacity of 1000 kN to examine eventual degradation of the measurement accuracy with respect to the number of fatigue loading cycles. In addition, the experimental temperature correction procedure is proposed to obtain the temperature correction formula enabling to correct the effect of temperature on the load measurement.

Load-Measuring Pot Bearing with Built-In Load Cell —Part I: Design and Performance  [PDF]
Jeong-Rae Cho, Young Jin Kim, Jong-Won Kwark, Sung Yong Park, Won Jong Chin, Byung-Suk Kim
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.511104
Abstract:

This paper presents the underlying principle and the results of various performance evaluations for a load-measuring pot bearing with built-in load cell. The pot bearing composed of a pot made of steel in which an elastomer disk is inserted is a bearing supporting larger loads than the elastomeric bearing and accommodating rotational movement. Owing to a Poisson’s ratio close to 0.5, elastomer withstands hydrostatic pressure when confined in a rigid body. Accounting for this principle, the vertical load applied on the pot bearing can be obtained by converting the pressure acting on the elastomer. Therefore, a load-measuring pot bearing is developed in this study by embedding a load cell exhibiting remarkable durability in the base plate of the bearing. The details for the insertion of the load cell in the base plate of the pot were improved through finite element analysis to secure sufficient measurement accuracy. The evaluation of the static performance of the pot bearing applying these improved details verified that the bearing exhibited sufficient accuracy for the intended measurement purpose. The dynamic performance evaluation results indicated that accurate measurement of the dynamic load was also achieved without time lag.

An Iterative Algorithm for Generalized Mixed Equilibrium Problems and Fixed Points of Nonexpansive Semigroups  [PDF]
Jong Kyu Kim, Salahud din, Won Hee Won Hee
Journal of Applied Mathematics and Physics (JAMP) , 2017, DOI: 10.4236/jamp.2017.52025
Abstract:
In this works, by using the modified viscosity approximation method associated with Meir-Keeler contractions, we proved the convergence theorem for solving the fixed point problem of a nonexpansive semigroup and generalized mixed equilibrium problems in Hilbert spaces.
Performance of Block Space-Time Code in Wireless Channel Dynamics  [PDF]
Won Mee JANG, Jong Hak JUNG
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.26050
Abstract: In this work, we observe the behavior of block space-time code in wireless channel dynamics. The block space-time code is optimally constructed in slow fading. The block code in quasistatic fading channels provides affordable complexity in design and construction. Our results show that the performance of the block space-time code may not be as good as conventionally convolutional coding with serial transmission for some channel features. As channel approaches fast fading, a coded single antenna scheme can collect as much diversity as desired by correctly choosing the free distance of code. The results also point to the need for robust space-time code in dynamic wireless fading channels. We expect that self-encoded spread spec-trum with block space-time code will provide a robust performance in dynamic wireless fading channels.
A Study on the Wave Screening Effectiveness According to Trench Dimensions Using Ultrasonic Waves  [PDF]
Hee Seok Kim, Won Jong Chin
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.610061
Abstract: In this study numerical and experimental studies are conducted to examine the wave screening effectiveness of trenches. The numerical study relies on the finite element model of a sandbox with Lysmer-Kuhlemeyer absorbing boundaries. This model is used to examine the screening ef-fectiveness of trench studied for different trench dimensions and distances from the source and receiver to the trench. The results of the numerical analysis are compared with the results of the ultrasonic experiment performed on an acrylic block drilled with a rectangular cut. The comparison shows that the screening effectiveness of the trench is nearly equal if the depth of trench is larger than 60% of the surface wave length. It is also shown that if the distance between the trench and the source is longer than twice the surface wave length, the thickness of the trench does not affect the screening effectiveness.
Basic Research Articles in the Journal of the Korean Society of Plastic and Reconstructive Surgeons from 1974 to 2011
Jong Won Rhie
Archives of Plastic Surgery , 2012, DOI: http://dx.doi.org/10.5999/aps.2012.39.2.91
Abstract:
Self-Encoded Multiple Access Multiuser Convolutional Codes in Uplink and Downlink Cellular Systems  [PDF]
Jong Hak JUNG, Won Mee JANG, Lim NGUYEN
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2009, DOI: 10.4236/ijcns.2009.24027
Abstract: Self-encoded spread spectrum eliminates the need for traditional pseudo noise (PN) code generators. In a self-encoded multiple access (SEMA) system, the number of users is not limited by the number of available sequences, unlike code division multiple access (CDMA) systems that employ PN codes such as m-, Gold or Kassami sequences. SEMA provides a convenient way of supporting multi-rate, multi-level grades of service in multimedia communications and prioritized heterogeneous networking systems. In this paper, we propose multiuser convolutional channel coding in SEMA that provides fewer cross-correlations among users and thereby reducing multiple access interference (MAI). We analyze SEMA multiuser convolutional coding in additive white Gaussian noise (AWGN) channels as well as fading channels. Our analysis includes downlink synchronous system as well as asynchronous system such as uplink mobile-to-base station communication.
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