• 대한기계학회논문집A
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• 제34권7호
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• pp.843-850
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• 2010

지지격자체는 경수로 핵연료집합체의 가장 중요한 핵심 구조부품이다. 지지격자체 설계시의 고려사항은 원자로 운전중에 연료봉의 지지건전성을 유지하도록 하는 것이다. 본 연구에서는 연료봉이 유동기인진동에 의해서 진동할 때 연료봉과 연료봉 지지부 사이에서 상대변위를 완화해 줌으로서 연료봉의 프레팅 마모손상 가능성을 감소시킬 수 있는 이동 가능한 연료봉 지지부로 구성된 새로운 지지격자체 형상을 제안하였다. 아울러 제안된 이동 가능 지지부의 연료봉 지지특성을 유한요소해석을 통해 분석하였다.

• Earthquakes and Structures
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• 제23권4호
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• pp.373-384
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• 2022

To improve the seismic performance of suspended ceiling structures, various vibration-damping devices have been developed. However, the devices made of metals have a limit in that they cause large deformation and seriously damages the exterior of the suspended ceiling structure from the wall. As a results, their strengthening effect of the suspended ceiling structure was minimal. Thus, this study employed a spring and vibration-proof rubber effectively controlled vibrations without increasing horizontal seismic loads on the ceiling to enhance the seismic resistance of suspended ceiling structures. The objective of the study is to examine the dynamic properties of a seismic damping-isolation unit (SDI) with various details developed. The developed SDI was composed of a spring, embossed rubbers, and prestressed bolts, which were the main factors enhancing the damping effect. The shaking table tests were performed on eight SDI specimens produced with the number of layers of embossed rubber (n_s), presence or absence of a spring, prestressed force magnitude introduced in bolts (f_ps), and mass weight (W_m) as the main parameters. To identify the enhancement effect of the SDI, the dynamic properties of the control specimen with a conventional hanger bolt were compared to those of the SDI specimens. The SDI specimens were effective in reducing the maximum acceleration (A_{c max}), acceleration amplification factor (α_p), relative displacement (δ_R), and increasing the damping ratio (ξ) when compared to the control specimen. The A_{c max}, α_p, and δ_R of the SDI specimens with two rubbers, spring, and f_ps of 0.1f_by, where f_by is the yielding strength of the screw bolt were 57.8%, 58.0%, and 61.9% lower than those of the conventional hanger bolt specimens, respectively, resulting in the highest ξ (=0.127). In addition, the α_p of the SDI specimens was 50.8% lower than those specified in ASCE 7 and FEMA 356. Consequently, to accurately estimate the α_p of the SDI specimens, a simple model was proposed based on the functions of f_ps, stiffness constant of the spring (K), W_m, and n_s.

• Structural Engineering and Mechanics
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• 제63권2호
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• pp.147-160
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• 2017

In this study, the optimum parameters of Tuned Mass Dampers (TMDs) are proposed using Gravity Search Algorithm (GSA) and Particle Swarm Optimization (PSO) to reduce the responses of the structures. A MATLAB program is developed to apply the new approach to the benchmark 10 and 40-story structures. The obtained results are compared to those of other optimization methods used in the literature to verify the developed code. To show the efficiency and accuracy of the proposed methods, nine far-field and near-field worldwide earthquakes are applied to the structures. The results reveal that in the 40-story structure, GSA algorithm can reduce the Relative Displacement (RD) and Absolute Acceleration (AA) up to 43% and 21%, respectively while the PSO decreases them by 50% and 25%, respectively. In contrast, both GSA and PSO algorithms reduce the RD and AA about 29% and 21% for the 10-story structure. Furthermore, using the proposed approach the required TMD parameters reduce by 47% and 63% in the 40 and 10-story buildings in comparison with the referenced ones. Result evaluation and related comparison indicate that these methods are more effective even by using smaller TMD parameters resulting in the reduction of acting force from TMD, having smaller stiffness and damping factors while being more cost effective due to its decreased parameters. In other words, the TMD with optimum parameters can play a positive role in both tall and typical structures.

• Structural Engineering and Mechanics
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• 제61권5호
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• pp.675-684
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• 2017

In this paper, a hybrid seismic response control (HSRC) system was developed to control bridge behavior caused by the seismic load. It was aimed at optimum vibration control, composed of a rubber bearing of passive type and MR-damper of semi-active type. Its mathematical modeling was driven and applied to a bridge model so as to prove its validity. The bridge model was built for the experiment, a two-span bridge of 8.3 meters in length with the HSRC system put up on it. Then, inflicting the EI Centro seismic load on it, shaking table tests were carried out to confirm the system's validity. The experiments were conducted under the basic structure state (without an MR-damper applied) first, and then under the state with an MR-damper applied. It was also done under the basic structure state with a reinforced rubber bearing applied, then the passive on/off state of the HSRC system, and finally the semi-active state where the control algorithm was applied to the system. From the experiments, it was observed that pounding rather increased when the MR-damper alone was applied, and also that the application of the HSRC system effectively prevented it from occurring. That is, the experiments showed that the system successfully mitigated structural behavior by 70% against the basic structure state, and, further, when control algorithm is applied for the operation of the MR-damper, relative displacement was found to be effectively mitigated by 80%. As a result, the HSRC system was proven to be effective in mitigating responses of the two-span bridge under seismic load.

• 비파괴검사학회지
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• 제26권2호
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• pp.122-129
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• 2006

본 논문에서는 레이저 응용 비파괴검사 기술인 Shearography를 이용하여 압력 배관 내부 결함의 검출에 있어서 미치는 전단량의 영향을 분석하였다. Shearography는 레이저 응용기법에 비하여 환경 외란에 둔감하며, 대상체 표면의 상대 변위를 검출함으로서 비파괴검사 분야에서 많은 활용이 기대된다. 현재까지 연구는 적용 가능성의 평가와 적용 대상의 확대에 중점을 두어 연구가 진행되어 왔으며, 결함의 정량평가를 위해서는 결함 검출에 있어서 영향을 주는 인자들에 대한 연구가 필요하다. 따라서 본 논문에서는 결함의 검출에 영향을 줄 수 있는 전단량의 변화에 따라 결함의 크기 측정과 길함의 위치 결정에 대한 영향을 예측하고, 압력용기 내부의 길이 방향 인공 결함에 대해 적용하여 검출 결과를 분석하였다.

• 대한기계학회논문집A
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• 제35권2호
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• pp.201-206
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• 2011

지지격자체는 경수로 핵연료집합체의 특성과 성능에 영향을 주는 가장 중요한 핵심 구조부품 중에 하나이다. 지지격자체 설계시의 우선적으로 고려해야할 사항은 핵연료가 원자로에 장전되어 있는 동안 내내 연료봉이 기계적인 원인에 의해 손상되지 않도록, 즉 연료봉의 기계적 지지건전성이 유지되도록 설계하는 것이다. 연료봉이 유동기인진동에 의해서 진동할 때 연료봉과 연료봉 지지부 사이에서 상대변위 발생을 완화해 줌으로서 연료봉의 프레팅 마모 손상 가능성이 감소될 수 있는 것으로 알려져 있다. 본 연구에서는 이동 가능한 연료봉 지지부로 구성된 새로운 지지격자체 형상을 제안하였고, 제안된 이동 가능 지지부의 연료봉 지지특성을 유한요소해석을 통해 분석하였다.

• 소음진동
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• 제8권2호
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• pp.260-266
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• 1998

수조 내에 잠긴 구조물에 대한 미끄럼 지진응답의 해석시 비선형 모델에 포함되는 유체동적 효과를 계산할 때에 종래의 방법은 수조와 구조물 사이의 초기 간격 조건만으로 계산한 다음, 이를 지진 작용 시간동안 일정한 값으로 가정하여 사용하였다. 이는 지진시 수중구조물의 예상변위가 유체 간격에 비해 아주 작다고 가정하였기 때문이다. 그러나 유체 간격이 비교적 크지 않은 조건에서는 이 방법은 자칫 비보수적인 결과를 초래할 수 있다. 본 논문에서는 건물내 수조에 잠긴 구조물에 대한 지진해석의 한가지 예를 통하여 어떠한 경우 얼마나 미끄럼변위를 과소평가 할 수 있는지를 보인다. 그리고, 이러한 경우 최대 미끄럼변위의 예측시 예상되는 과도한 오차를 피하기 위하여는 시간적분을 위한 각 적분 단위시간마다 유체동적 효과를 지속적으로 계산하여 개정하여 주어야 한다는 사실을 확인하였다.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.589-599
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• 2024

This study presents the usability of the high-rate single-frequency Precise Point Positioning (SF-PPP) technique based on 20 Hz Global Positioning Systems (GPS)-only observations in detecting dynamic motions. SF-PPP solutions were obtained from post-mission and real-time GNSS corrections. These include the International GNSS Service (IGS)-Final, IGS real-time (RT), real-time MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis), and real-time products from the Australian/New Zealand satellite-based augmentation systems (SBAS, known as SouthPAN). SF-PPP results were compared with LVDT (Linear Variable Differential Transformer) sensor and single-frequency relative positioning (SF-RP) solutions. The findings show that the SF-PPP technique successfully detects the harmonic motions, and the real-time products-based PPP solutions were as accurate as the final post-mission products. In the frequency domain, all GNSS-based methods evaluated in this contribution correctly detect the dominant frequency of short-term harmonic oscillations, while the differences in the amplitude values corresponding to the peak frequency do not exceed 1.1 mm. However, evaluations in the time domain show that SF-PPP needs high-pass filtering to detect accurate displacement since SF-PPP solutions include trends and low-frequency fluctuations, mainly due to atmospheric effects. Findings obtained in the time domain indicate that final, real-time, and MADOCA-based PPP results capture short-term dynamic behaviors with an accuracy ranging from 3.4 mm to 8.5 mm, and SBAS-based PPP solutions have several times higher RMSE values compared to other methods. However, after high-pass filtering, the accuracies obtained from PPP methods decreased to a few mm. The outcomes demonstrate the potential of the high-rate SF-PPP method to reliably monitor structural and earthquake-induced ground motions and vibration frequencies of structures.