• 한국항해항만학회지
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• 제36권2호
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• pp.89-95
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• 2012

Identification of the modal properties of a structural system has received much attention over the years because of its importance in structural model updating, structural health monitoring and structural control. This paper presents experimental modal test results such as natural frequencies and mode shapes of a scale model of floating structure. A modal testing is performed on the structure and modal parameters for the structure are extracted from the measured data. The results are compared to a finite element model and the correlation between the measured and analytical modal parameters is investigated.

• 한국정밀공학회지
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• 제16권11호
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• pp.183-190
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• 1999

In this paper, a dynamic modeling approach is introduced to identify the dynamic characteristics of the structural/mechanical joints within an one-dimensional structure. A structural joint is represented by the four-pole parameters and the four-pole parameters are determined from the measured frequency response functions by using the spectral element method. As the illustrative examples, a cantilevered beam a clamped-clamped beam, both consist of two beams connected by a bolted joint, are investigated to evaluate the present modeling approach. It is found that the dynamic responses predicted by using the identified for-pole parameters for the bolted joint are well agreed with the measured dynamic responses measured

• Smart Structures and Systems
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• 제7권5호
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• pp.349-363
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• 2011

To assess the performance of a structure requires the measurement of global and relative displacements at critical points across the structure. They should be obtained in real time and in all weather condition. A Global Navigation Satellite System (GNSS) could satisfy the last two requirements. The American Global Position System (GPS) provides long term acquisitions with sampling rates sufficient to track the displacement of long period structures. The accuracy is of the order of sub-centimetres. The steel building which hosts the authors' laboratory is the reference case-study within this paper. First a comparison of data collected by GPS sensor units with data recorded by tri-axial accelerometers is carried out when dynamic vibrations are induced in the structure by movements of the internal bridge-crane. The elaborations from the GPS position readings are then compared with the results obtained by a Finite Element (FE) numerical simulation. The purposes are: i) to realize a refinement of the structural parameters which characterize the building and ii) to outline a suitable way for processing GPS data toward structural monitoring.

• 대한안전경영과학회지
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• 제23권4호
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• pp.67-72
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• 2021

To ensure the safety and functionality of a railroad bridge, maintaining the integrity of the bridge via continuous structural health monitoring is important. However, most structural integrity monitoring methods proposed to date are based on modal responses which require the extracting process and have limited availability. In this paper, the applicability of the existing damage identification method based on free-vibration reponses to time-domain deflection shapes due to moving train load is investigated. Since the proposed method directly utilizes the time-domain responses of the structure due to the moving vehicles, the extracting process for modal responses can be avoided, and the applicability of structural health evaluation can be enhanced. The feasibility of the presented method is verified via a numerical example of a simple plate girder bridge.

• Advances in nano research
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• 제11권6호
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• pp.641-648
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• 2021

In this article, the dynamic parameters (frequencies, mode shapes, damping ratios) of the scaled concrete structure and the dynamic parameters (frequencies, mode shapes, damping ratios) of the entire outer surface of titanium dioxide, 80 micron in thickness are compared using operational modal analysis method. Ambient excitation was provided from micro tremor ambient vibration data on ground level. Enhanced Frequency Domain Decomposition (EFDD) was used for the output only modal identification. From this study, a good correlation between mode shapes was found. Titanium dioxide applied to the entire outer surface of the scaled concrete structure has an average of 11.78% difference in frequency values and 10.15% in damping ratios, proving that nanomaterials can be used to increase rigidity in structures, in other words, for reinforcement. Another important result determined in the study was the observation of the adherence of titanium dioxide and similar nanomaterials mentioned in the introduction to concrete structure surfaces was at the highest level.

• Advances in nano research
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• 제12권1호
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• pp.65-72
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• 2022

The dynamic properties (frequencies, mode shapes, damping ratios) of the scaled WPC warehouse are compared using the operational modal analysis approach to the dynamic parameters (frequencies, mode shapes, damping ratios) of the full outer surface of titanium dioxide, 70 micron in thickness. Micro tremor ambient vibration data on ground level was used to provide ambient excitation. For the output-only modal identification, Enhanced Frequency Domain Decomposition (EFDD) was used. This study discovered a strong correlation between mode shapes. Titanium dioxide applied to the entire outer surface of the scaled WPC warehouse results in an average 14.05 percent difference in frequency values and 7.61 percent difference in damping ratios, demonstrating that nanomaterials can be used to increase rigidity in structures, or for reinforcement. Another significant finding in the study was the highest level of adherence of titanium dioxide and similar nanomaterials mentioned in the introduction to WPC structure surfaces.

• Structural Monitoring and Maintenance
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• 제10권1호
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• pp.63-86
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• 2023

Structural health monitoring and damage detection are essential for assessing, maintaining, and rehabilitating structures. Most of the existing damage detection approaches compare the current state structural response with the undamaged vibrational structural response, which is unsuitable for old and existing structures where undamaged vibrational responses are absent. One of the approaches for existing structures, numerical model updating/inverse modelling, available in the literature, is limited to numerical studies with high-end software. In this study, an attempt is made to study the effectiveness of the model updating technique, simplify modelling complexity, and economize its usability. The optimization-based detection problem is addressed by using programmable open-sourced code, OpenSees^® and a derivative-free optimization code, NOMAD^®. Modal analysis is used for damage identification of beam-like structures with several damage scenarios. The performance of the proposed methodology is validated both numerically and experimentally. The proposed method performs satisfactorily in identifying both locations and intensity of damage in structures.

• 드라이브 ㆍ 컨트롤
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• 제20권4호
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• pp.54-63
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• 2023

High and intermittent loading cycles induce fatigue damage to transmission components, resulting in premature gearbox failure. To identify gearbox defects, numerous vibration-based diagnostics techniques, using several artificial intelligence (AI) algorithms, have recently been presented. In this paper, an optimized deep belief network (DBN) model for gearbox problem diagnosis was designed based on time-frequency visual pattern identification. To optimize the hyperparameters of the model, a particle swarm optimization (PSO) approach was integrated into the DBN. The proposed model was tested on two gearbox datasets: a wind turbine gearbox and an experimental gearbox. The optimized DBN model demonstrated strong and robust performance in classification accuracy. In addition, the accuracy of the generated datasets was compared using traditional ML and DL algorithms. Furthermore, the proposed model was evaluated on different partitions of the dataset. The results showed that, even with a small amount of sample data, the optimized DBN model achieved high accuracy in diagnosis.

• 한국구조물진단유지관리공학회 논문집
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• 제17권6호
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• pp.61-69
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• 2013

본 연구에서는 준능동 진동 제어를 위한 MR 감쇠기의 동적 모델링을 통한 특성을 분석 및 평가하였다. 실제 구조물 크기의 모형구조물을 진동제어하기 위하여 Semi-active 성능의 MR Damper를 설계/제작 하였다. 일반적으로 MR Damper를 이용한 준능동 제어 시스템을 구축하기 위해서는 감쇠장치의 발생 감쇠력 및 거동 성향 등의 데이터를 수치적으로 나타낼 수 있는 동적 모델이 요구된다. 따라서 본 연구에서는 MR Damper의 동적거동을 예측/평가 할 수 있는 모델링을 하기 위하여 다양한 동적 모델 중 Power 모델 및 Bingham 모델을 적용하였다. 이때 동적 모델과 비교/평가하기 위하여 개발된 MR Damper의 동하중 실험을 수행하였다. 동하중 실험조건은 가진 주파수를 (0.15Hz, 1.0Hz, 2.0Hz) 선정하고, 주파수별 각각 3가지씩 가진 속도를 달리하여, 변위가 감쇠력에 미치는 영향력을 확인하였다. 이렇게 얻어진 MR Damper의 동하중실험 결과를 적용하여 각 동적 모델 별 모델변수를 규명하였고, 이를 바탕으로 힘-속도 관계곡선 및 예측된 발생 감쇠력을 산출하였으며, 산출된 결과와 개발된 MR Damper의 실험 결과를 상호 비교 평가하였다. 최종적으로 본 연구에서 개발한 MR Damper는 준능동 제어장치로 활용 가능함을 확인 하였고, 다양한 변위를 이용한 실험을 통하여 정상적인 진동제어를 위해서는 최소 2mm 이상의 변위가 확보되어야 한다는 결과를 얻었다.

• 한국항공우주학회지
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• 제43권8호
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• pp.757-764
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• 2015

본 논문에서는 소형 지구관측 위성의 광학카메라에 들어가는 미소진동을 보상하기 위한 초점면부 보정장치 시스템의 실험적 모델링을 수행하였다. 미소진동 외란을 보상하는 초점면부 보정장치의 구동기로 PZT 압전작동기를 적용하였다. 압전작동기는 히스테리시스 고유 특성을 갖게 되므로 보정장치 시스템의 정확한 수학적 모델링을 얻는데 어려움이 있다. 따라서 본 연구에서는 보정장치 시스템을 2차 선형시스템으로 가정하고 MATLAB의 시스템 식별 툴박스(System Identification Toolbox)를 이용하여 실험적으로 모델링을 수행하였다. 외란의 주파수 범위인 0~50Hz에서 응답 오차 10%를 만족하기 위해 단일 선형 모델로는 불가능하며 총 4개의 선형 모델이 필요하다. 각각의 모델은 0~50Hz 입력범위를 4개의 구간으로 나눈 영역에서 실제 동역학을 잘 표현 하고 있다. 미소진동 외란의 보상은 입력주파수에 따라 모델 스위칭 기법을 적용한 초점면부 보정장치 제어를 통해 이루어진다.