• 한국전산구조공학회논문집
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• 제29권4호
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• pp.355-362
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• 2016

대규모 지진에 대한 원전의 안전성을 확보하는 방안으로 기존 원전 구조물에 면진장치를 설치하는 방안이 도입되고 있다. 면진장치를 설치함으로써 상부구조와 지반의 거동을 격리시킬 수 있고, 구조물 자체의 고유주기가 길어지게 되는데, 이를 통해 지진하중에 대한 구조물의 응답을 감소시킬 수 있게 된다. 특히 원전구조물 설계 시 원전구조물 자체뿐만 아니라 원전 내부 기기에 대한 안전성 확보가 필수적이다. 이를 위해 특정 층에 위치한 기기의 설계를 위해 각 층의 최대 요구 응답을 나타내는 층응답스펙트럼이 일반적으로 사용된다. 본 논문에서는 원전 구조물의 지진해석을 통해 특정 층의 층응답스펙트럼을 평가하고, 면진 장치의 거동 특성중 하나인 2차 경화에 대한 영향 또한 평가하였다.

• 한국항행학회논문지
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• 제23권1호
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• pp.90-96
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• 2019

LPWA는 넓은 커버리지를 통해 구축비용 및 시간이 절감되는 기술이다. 하지만 LPWA는 UHF 전파를 사용하는 ISM 대역으로 직진성이 강해 실내에서는 성능이 매우 떨어지지만 실내에서도 다른 통신에 비해 높은 성능을 낼 수 있는 가능성이 있기 때문에 본 논문에서는 LPWA 기술 중 LoRa를 적용하여 실내 통신 성능을 측정하는 연구를 진행하였다. 이를 위해 4층에 데이터 수신 모듈을 설치한 후 동일 층부터 1층까지 건물의 끝에 송신 모듈을배치한 후 데이터를 수집하였다. 실험결과 1층 송신 모듈의 데이터를 98~99% 확률로 수집 가능하였으며 최저 RSSI는 약 -116 dBm을 나타내었다. 따라서 확산인자가 12일 때 최대 수신감도 -136 dBm을 갖는 LoRa의 스펙을 고려할 경우 산업현장 건물 내부의 LPWA 적용을 충분히 고려할 수 있을 것으로 기대된다.

• Steel and Composite Structures
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• 제47권4호
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• pp.489-502
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• 2023

The strong column-weak beam (SCWB) moment ratio is specified in AISC 341 to prevent an abrupt column sway in steel special moment frames (SMFs) during earthquakes. Even when the SCWB requirement is satisfied for an SMF, a column-sway can develop in the SMF. This is because the contribution of the composite beam action developed in the concrete floor slab and its supporting beams was not included while calculating the SCWB moment ratio. In this study, we developed a new method for calculating the SCWB moment ratio that included the contribution of composite beam action. We evaluated the seismic collapse performance of the SMFs considering various risk categories and building heights. We demonstrated that the collapse performance of the SMFs was significantly improved by using the proposed SCWB equation that also satisfied the target performance specified in ASCE 7.

• Geomechanics and Engineering
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• 제22권1호
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• pp.1-9
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• 2020

This paper presents an investigation of the ground response of a gob-side gateroad suffering mining stress induced by a 21 m-thick coal seam extraction. A field observation, including entry convergence and stress changes monitoring, was first conducted in the tailgate 8209. The observation results of entry convergence showed that, during the adjacent panel 8210 retreating period, the deformation of the gob-side gateroad experienced a continuous increase stage, subsequently, an accelerating increase stage, and finally, a slow increase stage. However, strong ground response, including roof bending deflection, rib extrusion and floor heave, occurred during the current panel 8209 retreating period, and the maximum floor heave reached 1530 mm. The stress changes within coal mass of the two ribs demonstrated that the gateroad was always located in the stress concentrated area, which responsible for the strong response of the tailgate 8209. Subsequently, a hydraulic fracture technique was proposed to pre-fracture the two hard roofs above the tailgate 8209, thus decreasing the induced disturbance on the tailgate. The validity of the above roof treatment was verified via field application. The finding of this study could be a reference for understanding the stability control of the gob-side gateroad in extra thick coal seams mining.

• Structural Engineering and Mechanics
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• 제39권1호
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• pp.1-20
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• 2011

This study investigates the feasibility of detecting structural damage using the HHT method. A damage detection index, the ratio of bandwidth (RB) is proposed. This index is highly correlated or approximately equal to the change of equivalent damping ratio for an intact structure incurring damage from strong ground motions. Based on an analysis of shaking table test data from benchmark models subjected to adjusted Kobe and El Centro earthquakes, the damage detection index is evaluated using the Hilbert-Huang Transform (HHT) and the Fast Fourier Transform (FFT) methods, respectively. Results indicate that, when the response of the structure is in the elastic region, the RB value only slightly changes in both the HHT and the FFT spectra. Additionally, RB values estimated from the HHT spectra vs. the PGA values change incrementally when the structure response is nonlinear i.e., member yielding occurs, but not in the RB curve from the FFT spectra. Moreover, the RB value of the top floor changes more than those from the other floors. Furthermore, structural damage is detected only when using the acceleration response data from the top floor. Therefore, the ratio of bandwidth RB estimated from the smoothed HHT spectra is an effective and sensitive damage index for detecting structural damage. Results of this study also demonstrate that the HHT is a powerful method in analyzing the nonlinear responses of steel structures to strong ground motions.

• Journal of Communications and Networks
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• 제5권4호
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• pp.354-364
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• 2003

A general method for the evaluation of the symbol error probability (SER) of ultra wideband (UWB) systems with various kind of modulation schemes (N-PAM, M-PPM, Bi-Orthogonal), in presence of multipath channel, multiuser and strong narrowband interference, is presented. This method is shown to be able to include all the principal multiaccess techniques proposed so far for UWB, time hopping (TH), direct sequence (DS) and optical orthogonal codes (OOC). A comparison between the performance of these multiple access and modulation techniques is given, for both ideal Rake receiver and minimum mean square error (MMSE) equalizer. It is shown that for all the analyzed multiple access schemes, a Rake receiver exhibits a high error floor in presence of narrowband interference (NBI) and that the value of the error floor is in-fluenced by the spectral characteristics of the spreading code. As expected, an MMSE receiver offers better performance, representing a promising candidate for UWB systems. When the multiuser interference is dominant, all multiple access techniques exhibit similar performance under high-load conditions. If the number of users is significantly lower than the spreading factor, then DS outperforms both TH and OOC. Finally 2PPM is shown to offer better performance than the other modulation schemes in presence of multiuser interference; increasing the spreading factor is proposed as a more effective strategy for SER reduction than the use of time diversity.

• 건축역사연구
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• 제26권1호
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• pp.61-70
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• 2017

We surveyed Preah Pithu monument group site in Angkor. We made the map of present condition throughout the actual measurement and 3D scan. And we restored the floor plan, and completed the map of site placement. During this processing, we confirmed the middle axis of temples and studied the relation of temples and made clear the order of sites. Throughout this studying, we verified the middle axis of sites is not matched in Preah Pithu monument group. It is different aspect comparing with general Khmer religion architectures which were built with the planification belonging to strong royal authority and shared main axis through whole sites. In other words, we can estimate that Preah Pithu monument group was not built with planification rather than expanded as occasional demand during the process of actual use.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.451-458
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• 2006

The goal of many researchers in the field of structural engineering is to reduce both damage to building structures and discomfort of their inhabitants during strong motion seismic events. The present paper reports on analytical work conducted with this aim in mind as a prior research of experimental study. A four-story, 6.4 m tall, laboratory model of a building is employed as a example structure. The laboratory structure has graphite epoxy columns and each floor is equipped with a chevron brace that serves to resist inter-story drift with the installation of a magnetorheological (MR) damper. An artificial excitation has been generated with a robust range of seismic characteristics. A series of numerical simulations demonstrates that an optimized fuzzy controller is capable of robust performance for a variety of seismic base motions. Optimization of the fuzzy controller is achieved using multi-objective genetic algorithm(MOGA), i.e. NSGA-II. Multiple objective functions are used in order to reduce both peak and root-means-squared displacement and accelerations at the floor levels of the building.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제28권6호
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• pp.484-487
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• 2002

Leiomyoma is a benign smooth muscle tumor that usually arise in the uterus, skin and gastrointestinal system. Only 2 percent are located in the head and neck. Leiomyomas of oral cavity are uncommon as only two cases have been reported in the Korean literature. The common location of oral cavity has been tongue, but other sites include buccal mucosa, lips, palate. mouth floor, and gingiva. Our patient was 30 years old female who complained of swelling and discomfort in the mouth floor. Microscopically this tumor showed bundles of intertwining spindle cells within fibrous connective tissue stroma. The nuclei were generally pale staining and blunt ended. Masson's trichrome stain was positive for muscle, and immunohistochemical study for ${\alpha}$-smooth muscle actin revealed strong positivity. It was treated by surgical excision. We experienced a case of leiomyoma of oral cavity, so we report with literature reviews

• 설비공학논문집
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• 제20권11호
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• pp.711-717
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• 2008

Despite the fact that UFAD(Under Floor Air Distribution) systems have many benefits and are being applied in the field in increasing numbers, there is a strong need for an improved fundamental understanding of several key performance features of these systems. This study numerically investigates the effect of supplied air temperature and supplied flow rate on the performance of UFAD, especially focused on thermal comfort. Also this study has compared UFAD with conventional overhead air distribution system. In contrast to the well-mixed room air conditions of the conventional overheat system, UFAD system produces an overall floor-to-ceiling airflow pattern that takes advantage of the natural buoyancy produced by heat sources in the occupied zone and more efficiently removes heat loads and contaminants from the space. Thermal comfort parameters were evaluated by CFD approach and then PMV was computed to detect the occupants' thermal sensation. Results show that radiative mean temperature plays crucial role on the evaluating PMV. Until now, the radiative temperature has been the missing link between CFD and thermal comfort, but the present study paves the way for overcoming this weakness.