• Smart Structures and Systems
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• 제25권1호
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• pp.47-56
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• 2020

This paper proposes a model-based approach for structural damage identification and quantification. Using pseudo modal strain energy and mode shape vectors, a damage-sensitive objective function is introduced which is suitable for damage estimation and quantification in shear frames. Whale optimization algorithm (WOA) is used to solve the problem and report the optimal solution as damage detection results. To illustrate the capability of the proposed method, a numerical example of a shear frame under different damage patterns is studied in both ideal and noisy cases. Furthermore, the performance of the WOA is compared with particle swarm optimization algorithm, as one the widely-used optimization techniques. The applicability of the method is also experimentally investigated by studying a six-story shear frame tested on a shake table. Based on the obtained results, the proposed method is able to assess the health of the shear building structures with high level of accuracy.

• 한국IT서비스학회지
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• 제8권1호
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• pp.113-124
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• 2009

Value-based requirements engineering process, called The ViRE(Value-Innovative Requirement Engineering) was suggested to create an uncontested market using ERRC(Eliminate, Reduce, Raise, Create) requirements analysis. But ViRE did not provides a quantitative data analysis method for ERRC decision so as to make objective decisions for customers. In this paper, to solve this problem, we suggest a quantitative ERRC analysis method by estimating requirements cost. Our method defines user requirements and decides their weight. Then, it makes quality level table for all the identified requirements and function modules and estimate implementation cost based on their quality levels. Finally, assess each requirement's impact and then evaluate ERRC value. We could get the more objective ERRC values by evaluate the requirement weight. functional module weight, and implementation cost. And we proved the efficiency of our model by a case study, smart student ID system.

• International journal of advanced smart convergence
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• 제8권2호
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• pp.183-190
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• 2019

In the era of the Fourth Industrial Revolution, digital transformation, which means changes in all industrial structures, politics, economics and society as well as IT technology, is an important issue. It is difficult to know which research topic is being studied because digital transformation is being studied in various fields. Convergence research is possible because a research topic is studied in various fields such as computer science area and Decision science area. However, it is difficult to know the specific research status of the research topic. In this study, eight research topics were derived using the topic modeling technique of text mining for abstract of academic literature and the trend of each topic was analyzed. We also proposed to create a Topic-Word Proportions Table in the LDA based Topic modeling process to predict the topic of new literature. The results of this study are expected to contribute to advanced convergence research on topic of digital transformation. It is expected that the literature related to each research topic will be grasped and contribute to the design of a new convergence research.

• Smart Structures and Systems
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• 제9권3호
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• pp.207-230
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• 2012

Full-scale shake table seismic experiments and low-amplitude vibration tests on a masonry building are carried out to assess its seismic performance as well as study the effectiveness of a new multifunctional textile material for retrofitting masonry structures against earthquakes. The un-reinforced and the retrofitted with glass fiber reinforced polymer (GFRP) strips masonry building was subjected to a series of earthquake excitations of increasing magnitude in order to progressively induce various small, moderate and severe levels of damage to the masonry walls. The performance of the original and retrofitted building states is evaluated. Changes in the dynamic characteristics (lowest four modal frequencies and damping ratios) of the building are used to assess and quantify the damage states of the masonry walls. For this, the dynamic modal characteristics of the structure states after each earthquake event were estimated by performing low-amplitude impulse hammer and sine-sweep forced vibration tests. Comparisons between the modal results calculated using traditional accelerometers and those using Fiber Bragg Grating (FBG) sensors embedded in the reinforcing textile were carried on to investigate the reliability and accuracy of FBG sensors in tracking the dynamic behaviour of the building. The retrofitting actions restored the stiffness characteristics of the reinforced masonry structure to the levels of the original undamaged un-reinforced structure. The results show that despite a similar dynamic behavior identified, corresponding to reduction of the modal frequencies, the un-reinforced masonry building was severely damaged, while the reinforced masonry building was able to withstand, without visual damage, the induced strong seismic excitations. The applied GFRP reinforcement architecture for one storey buildings was experimentally proven reliable for the most severe earthquake accelerations. It was easily placed in a short time and it is a cost effective solution (covering only 20% of the external wall surfaces) when compared to the cost for full wall coverage by GFRPs.

• Smart Structures and Systems
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• 제8권1호
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• pp.119-137
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• 2011

A bio-inspired two-mode structural health monitoring (SHM) system based on the Na$\ddot{i}$ve Bayes (NB) classification method is discussed in this paper. To implement the molecular biology based Deoxyribonucleic acid (DNA) array concept in structural health monitoring, which has been demonstrated to be superior in disease detection, two types of array expression data have been proposed for the development of the SHM algorithm. For the micro-vibration mode, a two-tier auto-regression with exogenous (AR-ARX) process is used to extract the expression array from the recorded structural time history while an ARX process is applied for the analysis of the earthquake mode. The health condition of the structure is then determined using the NB classification method. In addition, the union concept in probability is used to improve the accuracy of the system. To verify the performance and reliability of the SHM algorithm, a downscaled eight-storey steel building located at the shaking table of the National Center for Research on Earthquake Engineering (NCREE) was used as the benchmark structure. The structural response from different damage levels and locations was collected and incorporated in the database to aid the structural health monitoring process. Preliminary verification has demonstrated that the structure health condition can be precisely detected by the proposed algorithm. To implement the developed SHM system in a practical application, a SHM prototype consisting of the input sensing module, the transmission module, and the SHM platform was developed. The vibration data were first measured by the deployed sensor, and subsequently the SHM mode corresponding to the desired excitation is chosen automatically to quickly evaluate the health condition of the structure. Test results from the ambient vibration and shaking table test showed that the condition and location of the benchmark structure damage can be successfully detected by the proposed SHM prototype system, and the information is instantaneously transmitted to a remote server to facilitate real-time monitoring. Implementing the bio-inspired two-mode SHM practically has been successfully demonstrated.

• 한국ITS학회 논문지
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• 제11권2호
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• pp.102-110
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• 2012

저전력 근거리 통신을 목적으로 개발된 지그비 네트워크는 유비쿼터스 컴퓨팅을 위한 홈네트워크 솔루션으로 많이 활용되고 있다. 하지만 최근 스마트폰 및 타블렛 PC의 보급으로 인해 지그비 네트워크와 동일 주파수를 사용하는 무선랜의 사용이 증가하였고, 이로 인해 주파수 간섭 문제가 빈번히 발생하게 되었다. 이와 같은 주파수 간섭 문제를 해결하기 위해 지그비 네트워크에서의 간섭 최소화 기법의 연구가 활발히 진행되었다. 하지만 기존의 간섭 최소화 기법은 간섭탐지를 위한 자원 소모가 크거나 간섭 회피를 위한 채널 호핑 시간이 길다는 문제를 갖는다. 본 논문에서는 이러한 문제점을 개선하기 위한 방법을 제안한다. 제안하는 간섭 최소화 기법은 불필요한 자원의 낭비를 줄이기 위해 ACK 메커니즘을 이용하여 간섭을 탐지하며, 테이블 기반의 채널 호핑 기법을 통해 기존의 기법보다 빠르게 간섭을 회피한다. OPNET 시뮬레이터를 이용하여 제안하는 간섭 최소화 기법의 성능을 평가하였다. 실험 결과를 통해 간섭 발생시 제안하는 기법이 기존 기법보다 빠른 채널 호핑이 가능하고 이로 인해 네트워크의 성능을 향상시킬 수 있음을 확인하였다.

• Smart Structures and Systems
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• 제7권5호
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• pp.379-392
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• 2011

This paper presents a multi-functional system, consisting of a magnetorheological (MR) damper and an electromagnetic induction (EMI) device, and its applications in stay cables. The proposed system is capable of offering multiple functions: (1) mitigating excessive vibrations of cables, (2) estimating cable tension, and (3) harvesting energy for wireless sensors used health monitoring of cable-stayed bridges. In the proposed system, the EMI device, consisting of permanent magnets and a solenoid coil, can converts vibration energy into electrical energy (i.e., induced emf); hence, it acts as an energy harvesting system. Moreover, the cable tension can be estimated by using the emf signals obtained from the EMI device. In addition, the MR damper, whose damping property is controlled by the harvested energy from the EMI device, can effectively reduce excessive cable vibrations. In this study, the multi-functionality of the proposed system is experimentally evaluated by conducting a shaking table test as well as a full-scale stay cable in a laboratory setting. In the shaking table experiment, the energy harvesting capability of the EMI device for wireless sensor nodes is investigated. The performance on the cable tension estimation and the vibration mitigation are evaluated using the full-scale cable test setup. The test results show that the proposed system can sufficiently generate and store the electricity for operating a wireless sensor node twice per day, significantly alleviate vibration of a stay cable (by providing about 20% larger damping compared to the passive optimal case), and estimate the cable tension accurately within a 2.5% error.

• Smart Structures and Systems
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• 제31권1호
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• pp.89-100
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• 2023

This paper conducts a parametric study of a new tuned mass damper with pre-strained superelastic SMA helical springs (SMAS-TMD) on the vibration reduction effect. First, a force-displacement relation model of superelastic SMA helical spring is presented based on the multilinear constitutive model of SMA material, and the tension tests of the six SMA springs fabricated are implemented to validate the mechanical model. Then, a dynamic model of a single floor steel frame with the SMAS-TMD damper is set up to simulate the seismic responses of the frame, which are testified by the shaking table tests. The wire diameter, initial coil diameter, number of coils and pre-strain length of SMA springs are extracted to investigate their influences on the seismic response reduction of the frame. The numerical and experimental results show that, under different earthquakes, when the wire diameter, initial coil diameter and number of coils are set to the appropriate values so that the initial elastic stiffness of the SMA spring is between 0.37 and 0.58 times of classic TMD stiffness, the maximum reduction ratios of the proposed damper can reach 40% as the mass ratio is 2.34%. Meanwhile, when the pre-strain length of SMA spring is in a suitable range, the SMAS-TMD damper can also achieve very good vibration reduction performance. The vibration reduction performance of the SMAS-TMD damper is generally equal to or better than that of the classic optimal TMD, and the proposed damper effectively suppresses the detuning phenomena that often occurs in the classic TMD.

• Smart Structures and Systems
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• 제32권5호
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• pp.281-295
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• 2023

The purpose of this study is to demonstrate and verify the application of phase-control absolute-acceleration-feedback active tuned mass dampers (PCA-ATMD) to multiple-degree-of-freedom (MDOF) building structures. In addition, servo speed control technique has been developed as a replacement for force control in order to mitigate the negative effects caused by friction and inertia. The essence of the proposed PCA-ATMD is to achieve a 90° phase lag for a structure by implementing the desired control force so that the PCA-ATMD can receive the maximum power flow with which to effectively mitigate the structural vibration. An MDOF building structure with a PCA-ATMD and a real-time filter forming a complete system is modeled using a state-space representation and is presented in detail. The feedback measurement for the phase control algorithm of the MDOF structure is compact, with only the absolute acceleration of one structural floor and ATMD's velocity relative to the structure required. A discrete-time direct output-feedback optimization method is introduced to the PCA-ATMD to ensure that the control system is optimized and stable. Numerical simulation and shaking table experiments are conducted on a three-story steel shear building structure to verify the performance of the PCA-ATMD. The results indicate that the absolute acceleration of the structure is well suppressed whether considering peak or root-mean-square responses. The experiment also demonstrates that the control of the PCA-ATMD can be decentralized, so that it is convenient to apply and maintain to real high-rise building structures.

• 한국유통학회지:유통연구
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• 제17권4호
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• pp.1-27
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• 2012

본 연구는 3대 대형마트(이마트, 홈플러스 및 롯데마트)의 점포이미지 구성요인이 쇼핑가치 및 쇼핑만족에 미치는 영향을 분석하였다. 점포이미지 구성요인으로 점포분위기, 판매원서비스, 부대시설, 제품구색 및 점포입지를 포함하였고, 쇼핑가치로는 실용적 쇼핑가치 및 쾌락적 쇼핑가치 등을 포함하였다. 자료는 지방에 위치한 세 점포를 이용하는 쇼핑객 114명을 대상으로 'mall-intercept' 방법에 의해 수집한 다음, SmartPLS 2.0에 의해 분석하였다. 분석결과, 판매원서비스 및 점포입지가 실용적 쇼핑가치에 영향을 주고, 점포분위기, 판매원서비스 및 점포입지가 쾌락적 쇼핑가치에 영향을 주는 것으로 나타났다. 쇼핑가치들은 모두 쇼핑만족에 영향을 주는 것으로 나타났다. 이들 두 쇼핑가치 가운데 쾌락적 쇼핑가치가 쇼핑만족에 더 많은 영향을 주는 것으로 나타났다. 본 연구는 지각된 혼잡이 쇼핑가치와 쇼핑만족 간의 관계에 대해 조절역할을 하는지 분석하였다. 분석결과, 쇼핑가치와 쇼핑만족 간의 관계에서 지각된 혼잡이 조절역할을 하지 않는 것으로 나타났다. 이는 쇼핑가치와 쇼핑만족 간의 관계에서 지각된 혼잡의 정도에 따라 이들 관계의 크기가 크게 변하지 않음을 의미한다. 지각된 혼잡의 조절역할 외에, 지각된 혼잡이 쇼핑만족에 직접영향을 줄 것으로 가정하고 이를 WarpPLS 3.0에 의해 분석한 결과, 두 변수 간에는 비선형 관계(non-linear)가 있음이 밝혀졌다. 즉 점포혼잡을 크게 지각할수록 쇼핑만족은 더 크게 증가하는 것으로 나타났다. 본 연구가 기존의 연구와 다른 차별점은 이들 간의 관계에서 지각된 혼잡의 역할을 중점적으로 분석하였다는 점이다. 본 연구는 점포이미지가 쇼핑만족에 미치는 직접효과도 분석하였다. 즉 소비자가 지각하는 점포에 대한 이미지가 쇼핑가치를 매개하지 않고 쇼핑만족에 직접 영향을 주는가를 분석하였다. 분석결과, 점포분위기와 판매원서비스가 쇼핑만족에 직접 영향을 주는 것으로 나타났다. 이러한 연구결과를 토대로 실무적 시사점, 연구의 한계 및 향후의 연구방향 등에 대해 기술하였다.