• Smart Structures and Systems
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• v.4 no.6
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• pp.795-807
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• 2008

A challenging problem in structural damage detection based on vibration data is the requirement of a large number of sensors and the numerical difficulty in obtaining reasonably accurate results when the system is large. To address this issue, the substructure identification approach may be used. Due to practical limitations, the response data are not available at all degrees of freedom of the structure and the external excitations may not be measured (or available). In this paper, an adaptive damage tracking technique, referred to as the sequential nonlinear least-square estimation with unknown inputs and unknown outputs (SNLSE-UI-UO) and the sub-structure approach are used to identify damages at critical locations (hot spots) of the complex structure. In our approach, only a limited number of response data are needed and the external excitations may not be measured, thus significantly reducing the number of sensors required and the corresponding computational efforts. The accuracy of the proposed approach is illustrated using a long-span truss with finite-element formulation and an 8-story nonlinear base-isolated building. Simulation results demonstrate that the proposed approach is capable of tracking the local structural damages without the global information of the entire structure, and it is suitable for local structural health monitoring.

• Structural Engineering and Mechanics
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• v.71 no.6
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• pp.751-761
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• 2019

Lamb wave technology is a promising technology in the field of structural health monitoring and can be applied in the detection and monitoring of defects in plate structures. Based on the reconstruction algorithm for the probabilistic inspection of damage (RAPID), a Lamb-based detection and evaluation method of through-thickness rectangular notches in metal plates was proposed in this study. The influences of through-thickness rectangular notch length and the angle between sensing path and notch length direction on signals were further explored through simulations and experiments. Then a damage index calculation method which focuses on both phase and amplitude difference between detected signals and baseline signals was proposed. Based on the damage index difference between two vertically crossed sensing paths which pass through the notch in a sensor network, the notch direction identification method was proposed. In addition, the notch length was determined based on the damage index distribution along sensing paths. The experimental results showed that the image reconstructed with the proposed method could reflect the information for the evaluation of notches.

• Journal of the Korean Society of Safety
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• v.37 no.4
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• pp.92-100
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• 2022

Of the Korean military's 3,959 ammunition depots, 1,007 - more than 25% - violate safety requirements for distance and equipment. There is a risk of explosion in old depots that are vulnerable to various interior and exterior accidents. This paper examines 10 scenarios, with varying values for ammunition amount and safety distance. The study calculated the overpressure that can be applied to risk-exposure objects, based on the safety distance; expected damage was predicted using constructed spatial information from 3D explosion simulations. The simulations confirmed that explosion overpressure increased the most when the safety distance violation rate increased from 80% to 90%. It also confirmed that secondary damage such as fire and explosion can cause casualties and property damage when the violation rate is 60% or higher. The results show that building collapse becomes a risk with a violation rate of 70% or higher. We conclude that taking ammunition depot safety distance violation into account when planning military facilities and their land utilization could better protect life and property.

• Steel and Composite Structures
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• v.42 no.2
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• pp.151-159
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• 2022

This study discusses a hypothetical method for tracking the propagation damage of Carbon Reinforced Fiber Plastic (CRFP) components underneath vibration fatigue. The High Cycle Fatigue (HCF) behavior of composite materials was generally not as severe as this of admixture alloys. Each fissure initiation in metal alloys may quickly lead to the opposite. The HCF behavior of composite materials is usually an extended state of continuous degradation between resin and fibers. The increase is that any layer-to-layer contact conditions during delamination opening will cause a dynamic complex response, which may be non-linear and dependent on temperature. Usually resulted from major deformations, it could be properly surveyed by a non-contact investigation system. Here, this article discusses the scanning laser application of that vibrometer to track the propagation damage of CRFP components underneath fatigue vibration loading. Thus, the study purpose is to demonstrate that the investigation method can implement systematically a series of hypothetical means and dynamic characteristics. The application of the relaxation method based on numerical simulation in the Artificial Intelligence (AI) Evolved Bat (EB) strategy to reduce the dynamic response is proved by numerical simulation. Thermal imaging cameras are also measurement parts of the chain and provide information in qualitative about the temperature location of the evolution and hot spots of damage.

• Smart Structures and Systems
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• v.32 no.1
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• pp.49-59
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• 2023

A bridge transportation network supplies products from various source nodes to destination nodes through bridge structures in a target region. However, recent frequent earthquakes have caused damage to bridge structures, resulting in extreme direct damage to the target area as well as indirect damage to other lifeline structures. Therefore, in this study, a surrogate model-based comprehensive framework to estimate the seismic resilience of bridge transportation networks is proposed. For this purpose, total system travel time (TSTT) is introduced for accurate performance indicator of the bridge transportation network, and an artificial neural network (ANN)-based surrogate model is constructed to reduce traffic analysis time for high-dimensional TSTT computation. The proposed framework includes procedures for constructing an ANN-based surrogate model to accelerate network performance computation, as well as conventional procedures such as direct Monte Carlo simulation (MCS) calculation and bridge restoration calculation. To demonstrate the proposed framework, Pohang bridge transportation network is reconstructed based on geographic information system (GIS) data, and an ANN model is constructed with the damage states of the transportation network and TSTT using the representative earthquake epicenter in the target area. For obtaining the seismic resilience curve of the Pohang region, five epicenters are considered, with earthquake magnitudes 6.0 to 8.0, and the direct and indirect damages of the bridge transportation network are evaluated. Thus, it is concluded that the proposed surrogate model-based framework can efficiently evaluate the seismic resilience of a high-dimensional bridge transportation network, and also it can be used for decision-making to minimize damage.

• Journal of the Society of Disaster Information
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• v.14 no.3
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• pp.262-270
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• 2018

Purpose: This paper investigates and analyzes the loss and damage ratio of maintenance monitoring sensor in metropolitan and high speed railroad tunnel in Korea and abroad. Method: After 5~6 years from the installation, the maintenance monitoring sensor on metropolitan transit tunnels showed the loss and damage ratio from 14.2% to 14.8% in Seoul metro line no. 5, 6, 7, 9, and 13.9% in UK channel tunnel. Based on the result, 15% is thought to be a proper set for the elapsed years, which is 5 years from the installation. Results: The maintenance monitoring sensor on high speed railroad tunnels showed the loss and damage ratio of 60.9% in Ho-Nam high speed railroad on 1 stage after 3 ~ 5 years from the installation, which was approximately 4 times as high as that of Seoul metro line no. 5, 6, 7, 9. Conclusion: Kyung-Bu high speed railroad on 2 stage, after 8~10 years from the installation, showed the loss and damage ratio of 66.8%. Based on the result, it can be inferred that the loss and damage ratio increases drastically after 5~10 years from the installation. Therefore, it is necessary to study on the loss and damage ratio of long term elapsed years, especially more than 10 years from the installation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.981-983
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• 2013

Damage of the road flooding has recently increased because of torrential rains. However, its prevention is in poor situation. In this study, we propose system expressing an information of flood risk for announcing to drivers to prevent damage of flooding or traffic jams. Our system implements on GUI enviroment that users can easily know the danger of road flooding using C# Language and ArcObjects API. If users use this system, they can know how dangerous of flooding.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.810-816
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• 2017

This study investigates the relationship between the damage patterns and structural performance levels of a multi-strand 7-wire strand that is used as an important member of stay cables. Stay cables are continuously damaged after completion, and corrosion is the main cause. However, it is difficult to check the damage pattern inside the cable due to its structural characteristics, and it is difficult to evaluate the degradation level of the damage quantitatively. This study derives the relationship between the damage pattern and the performance level of the stranded wire by comparing results and analyzing them through an indoor experiment and finite element analysis. In order to simulate the damage of a 7-wire strand, artificial damage was applied by mechanical precision machining to perform a performance evaluation. The results of the analysis show that regardless of the damage size of the strand, the structural performance deteriorated immediately after the damage. It was experimentally and analytically deduced that the type and amount of damage should be considered as a parameter for evaluating the performance level of the strand. This information can be used for the safety management of a cable stayed bridge by constructing a database according to the pattern and amount of damage.

• Korean Journal of Remote Sensing
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• v.35 no.6_2
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• pp.1133-1148
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• 2019

Tree growth and vitality in forest shows seasonal changes. So, in order to detect forest damage accurately, we have to use satellite images before and after damages taken at the same season. However, temporal resolution of high or medium resolution images is very low,so it is not easy to acquire satellite images of the same seasons. Therefore, in this study, we estimated spectral information of the same DOY using time-series Landsat images and used the estimates as reference values to assess forest damages. The study site is Hwasun, Jeollanam-do, where forest damage occurred due to hail and drought in 2017. Time-series vegetation index (NDVI, EVI, NDMI) maps were produced using all Landsat 8 images taken in the past 3 years. Daily normal vegetation index maps were produced through cloud removal and data interpolation processes. We analyzed the difference of daily normal vegetation index value before damage event and vegetation index value after event at the same DOY, and applied the criteria of forest damage. Finally, forest damage map based on daily normal vegetation index was produced. Forest damage map based on Landsat images could detect better subtle changes of vegetation vitality than the existing map based on UAV images. In the extreme damage areas, forest damage map based on NDMI using the SWIR band showed similar results to the existing forest damage map. The daily normal vegetation index map can used to detect forest damage more rapidly and accurately.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1374-1379
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• 2015

Malicious network attacks such as DDoS has no clear measures, the damage is also enormous. In particular, in addition to a network failure, such as leakage of personal information and damage of the communication charge in the case of zombie smartphone is infected, is expected damages of various users. In this study, we extract the zombie smartphone's phenomena and features that appear while the zombie service is running and introduce a corresponding technique to prevent zombie smartphone.