• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.5
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• pp.547-555
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• 2008

This parer proposed the path mismatch detection and compensation algorithm with closed form for linear amplification with non-linear components(LINC) system implementation. The LINC system has a merit of using the high efficient amplifier by transferring the non-constant envelop signal which is high peak to average signal ratio into constant envelop signal. However, the performance degradation is very sensitive to the path mismatch such as an amplitude mismatch and a phase mismatch. In order to improve the path mismatch, the error detection and compensation method is introduced by the use of four test signals. Since the presented method has the closed form solution, the efficient and fast detection is available. The digital-IF structure of LINC system applied by the proposed error detection and compensation algorithm was implemented. The performance was evaluated with the IEEE 802.16 WiMAX baseband sinal which has 7 MHz channel bandwidth and 16-QAM. The Error Vector Magnitude(EVM) of -37.37 dB was obtained through performance test, which meets performance requirement of -24 dB EVM. As a result, the introduced error detection and compensation method was verified to improve the LINC system performance.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1025-1037
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• 2015

Flexible base isolation bearings that separate superstructure from ground have been widely used in the construction field because they make a significant contribution to increasing the fundamental period of the structure, thereby decreasing response acceleration transmitted into the superstructure. However, the established bearing devices installed to uphold the whole building give rise to some problems involved with failure and collapse due to lack of the capacity as modern structures are getting more massive and higher. Therefore, this study suggests new isolation bearings assembled with additional restrainers enabled to reinforcing and recentering, and then evaluates their performance to withstand the seismic load. The superelastic shape memory alloy (SMA) bars are installed into the conventional lead-rubber bearing (LRB) devices in order to provide recentering forces. These new systems are modeled as component spring models for the purpose of conducting nonlinear dynamic analyses with near fault ground motion data. The LRB devices with steel bars are also designed and analyzed to compare their responses with those of new systems. After numerical analyses, ultimate strength, maximum displacement, permanent deformation, and recentering ratio are compared to each model with an aim to investigate which base isolation models are superior. It can be shown that LRB models with superelastic SMA bars are superior to other models compared to each other in terms of seismic resistance and recentering effect.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.273-284
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• 2018

A detailed understanding of the mechanical behaviors for crushed coal rocks after grouting is a key for construction in the broken zones of mining engineering. In this research, experiments of grouting into the crushed coal rock using independently developed test equipment for solving the problem of sampling of crushed coal rocks have been carried out. The application of uniaxial compression was used to approximately simulate the ground stress in real engineering. In combination with the analysis of crack evolution and failure modes for the grouted specimens, the influences of different crushed degrees of coal rock (CDCR) and solidified grout strength (SGS) on the mechanical behavior of grouted specimens under uniaxial compression were investigated. The research demonstrated that first, the UCS of grouted specimens decreased with the decrease in the CDCR at constant SGS (except for the SGS of 12.3 MPa). However, the UCS of grouted specimens for constant CDCR increased when the SGS increased; optimum solidification strengths for grouts between 19.3 and 23.0 MPa were obtained. The elastic moduli of the grouted specimens with different CDCR generally increased with increasing SGS, and the peak axial strain showed a slightly nonlinear decrease with increasing SGS. The supporting effect of the skeleton structure produced by the solidified grouts was increasingly obvious with increasing CDCR and SGS. The possible evolution of internal cracks for the grouted specimens was classified into three stages: (1) cracks initiating along the interfaces between the coal blocks and solidified grouts; (2) cracks initiating and propagating in coal blocks; and (3) cracks continually propagating successively in the interfaces, the coal blocks, and the solidified grouts near the coal blocks. Finally, after the propagation and coalescence of internal cracks through the entire specimens, there were two main failure modes for the failed grouted specimens. These modes included the inclined shear failure occurring in the more crushed coal rock and the splitting failure occurring in the less crushed coal rock. Both modes were different from the single failure mode along the fissure for the fractured coal rock after grouting solidification. However, compared to the brittle failure of intact coal rock, grouting into the different crushed degree coal rocks resulted in ductile deformation after the peak strength for the grouted specimens was attained.

• Journal of Korea Water Resources Association
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• v.41 no.9
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• pp.959-967
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• 2008

Disaggregation techniques are widely used to transform observed daily rainfall values into hourly ones, which serve as important inputs for flood forecasting purposes. However, an important limitation with most of the existing disaggregation techniques is that they treat the rainfall process as a realization of a stochastic process, thus raising questions on the lack of connection between the structure of the models on one hand and the underlying physics of the rainfall process on the other. The present study introduces a nonlinear deterministic (and specifically chaotic) framework to study the dynamic characteristics of rainfall distributions across different temporal scales (i.e. weights between scales), and thus the possibility of rainfall disaggregation. Rainfall data from the Seoul station (recorded by the Korea Meteorological Administration) are considered for the present investigation, and weights between only successively doubled resolutions (i.e., 24-hr to 12-hr, 12-hr to 6-hr, 6-hr to 3-hr) are analyzed. The correlation dimension method is employed to investigate the presence of chaotic behavior in the time series of weights, and a local approximation technique is employed for rainfall disaggregation. The results indicate the presence of chaotic behavior in the dynamics of weights between the successively doubled scales studied. The modeled (disaggregated) rainfall values are found to be in good agreement with the observed ones in their overall matching (e.g. correlation coefficient and low mean square error). While the general trend (rainfall amount and time of occurrence) is clearly captured, an underestimation of the maximum values are found.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.173-173
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• 2010

$Bi_4Ti_3O_{12}$ ($B_4T_3$) is a unique ferroelectric material that has a relatively high dielectric constant, high Curie temperature, high breakdown strength, and large spontaneous polarization. As a result this material has been widely studied for many applications, including nonvolatile ferroelectric random memories, microelectronic mechanical systems, and nonlinear-optical devices. Several reports have appeared on the use of Mn dopants to improve the electrical properties of $B_4T_3$ thin films. Mn ions have frequently been used for this purpose in thin films and multilayer capacitors in situations where intrinsic oxygen vacancies are the major defects. However, no systematic study of the optical properties of $B_4T_3$ films has appeared to date. Here, we report optical data for these films, determined by spectroscopic ellipsometry (SE). We also report the effects of thermal annealing and Mn doping on the optical properties. The SE data were analyzed using a multilayer model that is consistent with the original sample structure, specifically surface roughness/$B_4T_3$ film/Pt/Ti/$SiO_2$/c-Si). The data are well described by the Tauc-Lorentz dispersion function, which can therefore be used to model the optical properties of these materials. Parameters for reconstructing the dielectric functions of these films are also reported. The SE data show that thermal annealing crystallizes $B_4T_3$ films, as confirmed by the appearance of $B_4T_3$ peaks in X-ray diffraction patterns. The bandgap of $B_4T_3$ red-shifts with increasing Mn concentration. We interpret this as evidence of the existence deep levels generated by the Mn transition-metal d states. These results will be useful in a number of contexts, including more detailed studies of the optical properties of these materials for engineering high-speed devices.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.661-668
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• 2009

Effective beam width model(EBWM) has been used for analysis of post-tensioned(PT) flat plate slab frames under lateral loads. The accuracy of this model in predicting lateral drifts and unbalanced moments strongly depends on the estimated effective stiffness of PT flat plate slabs. As moments on the slab due to lateral loads increases, cracks occur which leads to stiffness reduction in slabs. For analyzing PT flat plate slab structure under lateral loads with good precision, reduction in slab stiffness has to be accurately estimated for EBWM. For this purpose, this study collected test results of PT flat plate system conducted by former researches. And this study reduced the width of slab so that the stiffness of the EBWM converged into the lateral stiffness of each test specimens by trial and error. By conducting nonlinear regression analysis using the stiffness ratio of the reduced width of slab to the effective width of EBWM with respect to the level of slab moments, an equation for calculating stiffness reduction factor for slab is proposed. For verifying the accuracy of the proposed equation, this study compared with the test result of the PT flat plate frame. It is shown that the EBWM with the proposed equation predicts the actual stiffness of the PT specimen which varied according to the level of applied moment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.195-206
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• 2011

The capacity spectrum method(CSM) has been more frequently used as a tool to evaluate the seismic capacity of the structure. Many formulas of strength reduction factors(SRF) have been proposed and adopted to generate the inelastic demand spectrum for the CSM. This study evaluates the impacts of the type of the SRF on the inelastic demand spectrum and finally on the seismic response displacement of curved bridge. For the purpose, the several existing formulas of SRFs were comparatively investigated through the case study. Curved bridges with different subtended angles were selected and the displacements of the bridge piers were estimated by using the different formulas of SRFs. Nonlinear time history analyses were also performed for the validation purpose of the CSM results. According to study results, the CSM may generate the larger displacement responses than the actual behaviors for the curved bridge with larger subtended angles. Though many methods have been suggested to generate the inelastic demand spectrum for CSM, they might not give noticeable differences in inelastic displacement of the bridge pier.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.21-30
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• 2013

As increasing number of large-size earthquake, the social interest of seismic retrofitting of RC structure is growing. Especially, the RC columns that are not reflected seismic design can not resist lateral loads by the earthquake. The brittle fracture of Non-seismic designed columns lead to full collapse of the building. Thus, the emergency columns reinforcement method is needed. That have a fast construction time, do not cause damage to the column. In the past, cross-sectional expansion method, a steel plate reinforcing method is applied mainly, but in recent years, carbon fiber sheet taking advantage of FRP (Fiber Reinforced Polymer) is widely used. In this study, retrofitting effect of seismic performance of FRP seismic reinforcement, which is possible to emergency construction, was examined. Reinforced concrete specimens were constructed to experimental study. The seismic performence of specimes retrifitted with FRP seismic reinforcement were evaluated. As a result, the seismic performance of specimen reinforced with FRP seismic reinforcement has been improved.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.1
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• pp.46-51
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• 2014

The most important process of engineering system optimal design is to identify the relationship between the design variables and system response. In case of the system optimization, Response Surface Method (RSM) is widely used. The optimization process of RSM generates the design space using the typical alternative candidates and finds the optimal design point in the generated design space. By changing the optimal point depending on the configuration of the design space, it is important to generate the design space. Therefor in this study, the design space is generated by using the relationship between design variables and system response based on Neuro-Response Surface Method (NRSM). And I try to construct the framework for optimal shape design based on NRSM that the optimum shape can be predicted using the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) within the generated design space. In order to verify the usefulness of the constructed framework, we applied the nonlinear mathematical function problem. In this study, we can solve the constraints of time in the optimization process for the engineering problem and effective to determine the optimal design was possible. by using the generated framework for optimal shape design based on NRSM. In the future research, we try to apply the optimization problem for Naval Architectural & Ocean Engineering based on the results of this study.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.1
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• pp.17-26
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• 2009

The capacity spectrum method (CSM), which is known to be an approximate technique for assessing the seismic capacity of an existing structure, was originally proposed for simple building structures that could be modeled as single-degree-of-freedom (SDOF) systems. More recently, however, CSM has increasingly been adopted for assessing most bridge structures, as it has many practical advantages. Some studies on this topic are now being performed, and a few results of these have been presented as ground-breaking research. However, studies have until now been limited to symmetrical straight bridges only. This study evaluates the practical applicability of CSM to the evaluation of irregular curved bridges. For this purpose, the seismic capacities of 3-span prestressed concrete bridges with different subtended angles subjected to some recorded earthquakes are compared with a more refined approach based on nonlinear time history analysis. The results of the study show that when used for curved bridges, CSM induces higher inelastic displacement responses than the actual values, and that the gap between the two becomes larger as the subtended angle increases.