• Earthquakes and Structures
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• 제8권4호
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• pp.935-956
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• 2015

Structural Health Monitoring (SHM) of steel towers has become a hot research topic. From the literature, it is impractical and impossible to develop a "general" method that can detect all kinds of damages for all types of structures. A practical method should make use of the characteristics of the type of structures and the kind of damages. This paper reports a feasibility study on the use of measured modal parameters for the detection of damaged braces of tower structures following the Bayesian probabilistic approach. A substructure-based structural model-updating scheme, which groups different parts of the target structure systematically and is specially designed for tower structures, is developed to identify the stiffness distributions of the target structure under the undamaged and possibly damaged conditions. By comparing the identified stiffness distributions, the damage locations and the corresponding damage extents can be detected. By following the Bayesian theory, the probability model of the uncertain parameters is derived. The most probable model of the steel tower can be obtained by maximizing the probability density function (PDF) of the model parameters. Experimental case studies were employed to verify the proposed method. The contributions of this paper are not only on the proposal of the substructure-based Bayesian model updating method but also on the verification of the proposed methodology through measured data from a scale model of transmission tower under laboratory conditions.

• Journal of Photoscience
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• 제9권2호
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• pp.488-490
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• 2002

DNA photodamage mediated by photosensitizers are believed to play an important role in solar UVA carcinogenesis. We investigated the relationship between the DNA-damaging abilities of photoexcited xanthone analogues (as photosensitizers) and their highest occupied molecular orbital (HOMO) energies. DNA damage was examined using /sup 32/P-labeled DNA fragments obtained from the p53 tumor suppressor gene. These compounds induced DNA photodamage in a similar manner, and the extents of DNA damage were following order: xanthone> thioxanthone > acridone. Photoexcited xanthone caused nucleobase oxidation specifically at 5'-G of GG sequence in double-stranded DNA. An oxidative product of 2'-deoxyguanosine, 8-hydroxy-2'-deoxyguanosine (8-OHdG), was detected, and the amount was decreased by DNA denaturation. These findings suggest that photoexcited xanthone generates 8-OHdG at 5'-G of GG in double-stranded DNA through electron transfer. The calculated HOMO energies of these photosensitizers decreased in the following order: xanthone> thioxanthone > acridone. This study has demonstrated that DNA-damaging abilities of these photosensitizers increased exponentially with an increase in their HOMO energies.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.190-205
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• 2015

In this paper, the impact damage behavior of USN-150B carbon/epoxy composite laminates subjected to high velocity impact was studied experimentally and numerically. Square composite laminates stacked with $[45/0/-45/90]_{ns}$ quasi-symmetric and $[0/90]_{ns}$ cross-ply stacking sequences and a conical shape projectile with steel core, copper skin and lead filler were considered. First high-velocity impact tests were conducted under various test conditions. Three tests were repeated under the same impact condition. Projectile velocity before and after penetration were measured by infrared ray sensors and magnetic sensors. High-speed camera shots and C-Scan images were also taken to measure the projectile velocities and to obtain the information on the damage shapes of the projectile and the laminate specimens. Next, the numerical simulation was performed using explicit finite element code LS-DYNA. Both the projectile and the composite laminate were modeled using three-dimensional solid elements. Residual velocity history of the impact projectile and the failure shape and extents of the laminates were predicted and systematically examined. The results of this study can provide the understanding on the penetration process of laminated composites during ballistic impact, as well as the damage amount and modes. These were thought to be utilized to predict the decrease of mechanical properties and also to help mitigate impact damage of composite structures.

• 한국해양공학회지
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• 제33권3호
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• pp.259-271
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• 2019

It is important to obtain reasonable predictions of the extent of the damage during maritime accidents such as ship collisions and groundings. Many fracture models based on different mechanical backgrounds have been proposed and can be used to estimate the extent of damage involving ductile fracture. The goal of this study was to compare the damage extents provided by some selected fracture models. Instead of performing a new series of material constant calibration tests, the fracture test results for the ship building steel EH36 obtained by Park et al. (2019) were used which included specimens with different geometries such as central hole, pure shear, and notched tensile specimens. The test results were compared with seven ductile fracture surfaces: Johnson-Cook, Cockcroft-Latham-Oh, Bai-Wierzbicki, Modified Mohr-Coulomb, Lou-Huh, Maximum shear stress, and Hosford-Coulomb. The linear damage accumulation law was applied to consider the effect of the loading path on each fracture surface. The Swift-Voce combined constitutive model was used to accurately define the flow stress in a large strain region. The reliability of these simulations was verified by the good agreement between the axial tension force elongation relations captured from the tests and simulations without fracture assignment. The material constants corresponding to each fracture surface were calibrated using an optimization technique with the minimized object function of the residual sum of errors between the simulated and predicted stress triaxiality and load angle parameter values to fracture initiation. The reliabilities of the calibrated material constants of B-W, MMC, L-H, and HC were the best, whereas there was a high residual sum of errors in the case of the MMS, C-L-O, and J-C models. The most accurate fracture predictions for the fracture specimens were made by the B-W, MMC, L-H, and HC models.

• Smart Structures and Systems
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• 제31권3호
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• pp.229-245
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• 2023

The absence of excitation measurements may pose a big challenge in the application of structural damage identification owing to the fact that substantial effort is needed to reconstruct or identify unknown input force. To address this issue, in this paper, an iterative strategy, a synergy of Tikhonov regularization method for force identification and modified Jaya algorithm (M-Jaya) for stiffness parameter identification, is developed for damage identification with partial output-only responses. On the one hand, the probabilistic clustering learning technique and nonlinear updating equation are introduced to improve the performance of standard Jaya algorithm. On the other hand, to deal with the difficulty of selection the appropriate regularization parameters in traditional Tikhonov regularization, an improved L-curve method based on B-spline interpolation function is presented. The applicability and effectiveness of the iterative strategy for simultaneous identification of structural damages and unknown input excitation is validated by numerical simulation on a 21-bar truss structure subjected to ambient excitation under noise free and contaminated measurements cases, as well as a series of experimental tests on a five-floor steel frame structure excited by sinusoidal force. The results from these numerical and experimental studies demonstrate that the proposed identification strategy can accurately and effectively identify damage locations and extents without the requirement of force measurements. The proposed M-Jaya algorithm provides more satisfactory performance than genetic algorithm, Gaussian bare-bones artificial bee colony and Jaya algorithm.

• 한국압력기기공학회 논문집
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• 제11권2호
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• pp.61-67
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• 2015

3D FEM modeling based on 3D CAD data has been performed to evaluate the efficiency of CP system in a real operating nuclear power plant. The results of it successfully produced sophisticated profiles of electrolytic potential and current distributions in the soil of an interested area. This technology is expected to be a breakthrough for detection technology of damages on buried pipes when it comes into combining with a brand of area potential earth current (APEC) and ground penetrated radar (GPR) technologies. 2D current distribution and 2D current vectors on the earth surface from the APEC survey will be used as boundary conditions with exact 3D geometry data resulting in visualization of locations and extents of corrosion damages on the buried pipes in nuclear power plants.

• 대한조선학회지
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• 제27권4호
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• pp.72-82
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• 1990

해양구조물의 비보강원통 부재가 충돌로 인해 횡 충격하중을 받는 경우 비보강원통의 동적거동을 추적하고 그 결과로 발생되는 손상의 정도를 예측할 수 있는 간이 수치해석 방법을 제안하고자 한다. 이 방법에서는 국부적인 변형과 전체굽힘 변형을 별도로 자유도로 분리하여 2 자유도의 스프링-질량계로 치환하여 해석하게 된다. 변형속도를 비롯한 기타의 동적효과가 굽힘변형을 나타내는 스프링 상수값에 미치는 영향은 실험자료로부터 얻어진 수정계수를 도입하여 고려하였다. 제안된 해석방법을 사용하여 얻어진 손상정도의 값들은 실험결과와 비교적 잘 일치하고 있다.

• 한국해양공학회지
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• 제37권3호
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• pp.111-121
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• 2023

This paper intends to introduce the applicability of HydroQus to a problem of a tanker collision against a semi-submersible type floating offshore wind turbine (FOWT). HydroQus is a plug-in based on potential flow theory that generates interactive hydroforces in a commercial Finite element analysis (FEA) code Abaqus/Explicit. Frequency response analyses were conducted for a 10MW capacity FOWT to obtain hydrostatic and hydrodynamic constants. The tanker was modeled with rigid elements, while elastic-plastic elements were used for the FOWT. Mooring chains were modeled to implement station keeping ability of the FOWT. Two types of fracture models were considered: constant failure strain model and combined failure strain model HC-LN model composed of Hosford-Coulomb (HC) model & localized necking (LN) model. The damage extents were evaluated by hydroforces and failure strain models. The largest equivalent plastic strain observed in the cases where both restoring force and radiation force were considered. Stress triaxiality and damage indicator analysis showed that the application of HC-LN model was suitable. It could be stated that applications of suitable failure strain model and hydrodynamics into the collision simulations were of importance.

• 해양환경안전학회지
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• 제5권2호
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• pp.99-111
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• 1999

The object of this study is to get the superior double hull structure to its crashworthiness against collision comparing absorbed energy capacities of its various types with each other, varying material properties, collision positions and velocities, and structural arrangements such as double hull width, web and stringer spaces, etc. Local absorbed energy capacities, failure behaviors and damage extents of their members are also considered during collision in addition to the estimations of their global ones. This paper describes a series of numerical simulations of collisions between DWT 45,000 oil tanker(struck ship) and DWT 10,500 rigid one(striking ships) using Hydrocode LS/DYNA3D. Collisions are assumed to occur at the middle of struck ship with striking one moving at right angle to its centerline. The following remarks were obtained through this study: More flexible the double hull structure is, much superior its crashworthiness against collision is. The increment of double hull width does not give much influence than other factors do. The exact use of material property such as failure strain is also important on the numerical simulation of collision.

• Steel and Composite Structures
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• 제25권1호
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• pp.93-104
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• 2017

In the present work, the effect of hygrothermal aging on the glass fibre and epoxy matrix interface has been investigated by destructive and non-destructive techniques. The glass fiber reinforced polymer (GFRP) composite laminates were prepared using Vacuum Assisted Resin Infusion Molding (VARIM) technique and the specimens were immersed in simulated seawater, followed by quantitative measurement. Besides this, the tensile tests of GFRP specimens revealed a general decrease in the properties with increasing aging time. Also, exposed specimens were characterized by a non-destructive ultrasonic guided Lamb wave propagation technique. The experimental results demonstrate a correlation between the drop in ultrasonic voltage amplitude and fall in tensile strength with increasing time of immersion. Hence, the comparison of the transmitted guided wave signal of healthy vis-a-vis specimens subjected to different extents of hygrothermal aging facilitated performance evaluation of GFRP composites.