• International Journal of Concrete Structures and Materials
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• v.3 no.1
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• pp.33-37
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• 2009

Fiber Bragg grating (FBG) sensors already have been the focus for structural health monitoring (SHM) due to their distinguishing advantages. However, as bare optical fiber is very fragile, bare FBG strain sensor without encapsulation can not properly be applied in practical infrastructures. Therefore encapsulation techniques for making encapsulated FBG strain sensor show very important in pushing forward the application of FBG strain sensors in SHM. In this paper, a simplified approximate method to analyze the stress transferring rules for embedded FBG strain sensors in concrete monitoring is put forward according to mechanics of composite materials. Shear lag theory is applied to analyze the stress transferring rule of embedded FBG strain sensor in measured host material at the first time. The measured host objects (concrete) and the encapsulated FBG strain sensor are regarded as a composite, and then the stress transfer formula and stress transfer coefficient of encapsulated FBG strain sensor are obtained.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1061-1064
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• 2006

Optimal design of functionally graded plates is investigated considering stress and critical temperature. Material properties are assumed to be temperature dependent and varied continuously in the thickness direction. The effective material properties are obtained by applying linear rule of mixtures. The 3-D finite element model is adopted using an 18-node solid element to analyze more accurately the variation of material properties and temperature field in the thickness direction. For stress analysis, the tensile stress ratio and compressive stress ratio of the structure under mechanical load are investigated. In the thermo-mechanical buckling analysis, temperature at each node is obtained by solving the steady-state heat transfer problem and Newton-Raphson method is used for material nonlinear analysis. Finally, the optimal design of FGM plates is studied for stress reduction and improving thermo-mechanical buckling behavior, simultaneously.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.162-167
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• 2020

In this study, a fatigue analysis of an external fuel tank and pylon for fixed-wing aircraft was carried out as part of the domestic development of fixed-wing aircraft. Through structural analysis, the analysis areas were selected, and the transfer function for unit loads was established in the selected parts. For each of the continuous load profiles, stress components in the selected areas were calculated using the load of each profile and the transfer function, and the Von Mises equivalent stress was employed as the representative stress of each profile. In addition, the rainflow counting technique was used to extract individual profiles obtained from the initial large load profiles and to calculate their amplitude and average values. For life evaluation, the S-N diagram of the Metallic Materials Properties Development and Standardization (MMPDS) was applied, and the damage value was calculated by Miner's rule to assess the life of the selected area. As a result of the life assessment, the life span requirement for the selected area of the external fuel tank and the pylon was assessed as being satisfied.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.4
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• pp.239-251
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• 2015

In this study, a spectral fatigue analysis was performed for the topside structure of an offshore floating vessel. The topside structure was idealized using beam elements in the SACS program. The fatigue analysis was carried out considering the wave and wind loads separately. For the wave-induced fatigue damage calculation, motion RAOs calculated from a direct wave load analysis and regular waves with different periods and unit wave heights were utilized. Then, the member end force transfer functions were generated covering all the loading conditions. Stress response transfer functions at each joint were produced using the specified SCFs and member end force transfer functions. fatigue damages were calculated using the obtained stress ranges, S-N curve, wave spectrum, heading probability of each loading condition, and their corresponding occurrences in the wave scatter diagrams. For the wind induced fatigue damage calculation, a dynamic wind spectral fatigue analysis was performed. First, a dynamic natural frequency analysis was performed to generate the structural dynamic characteristics, including the eigenvalues (natural frequencies), eigenvectors (mode shapes), and mass matrix. To adequately represent the dynamic characteristic of the structure, the number of modes was appropriately determined in the lateral direction. Second, a wind spectral fatigue analysis was performed using the mode shapes and mass data obtained from the previous results. In this analysis, the Weibull distribution of the wind speed occurrence, occurrence probability in each direction, damping coefficient, S-N curves, and SCF of each joint were defined and used. In particular, the wind fatigue damages were calculated under the assumption that the stress ranges followed a Rayleigh distribution. The total fatigue damages were calculated from the combination with wind and wave fatigue damages according to the DNV rule.

• Journal of Ocean Engineering and Technology
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• v.34 no.2
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• pp.120-127
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• 2020

Evaluation of fatigue strength considering the springing effect of very large container ships is crucial in the design stage. In this study, we established a fatigue strength evaluation method considering a linear springing component in the frequency domain. Based on a three-dimensional global model, a fluid-structure interaction analysis was performed and the modal superposition method was applied to determine the hot spot stress at the hatch corner of very large container ships. Fatigue damage was directly estimated using the stress transfer function with a linear springing response. Furthermore, we proposed a new methodology to apply the springing effect to fatigue damage using hull girder loads. Subsequently, we estimated the fatigue damage contribution due to linear springing components along the ship length. Finally, we discussed the practical application of the proposed methods.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.435-446
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• 2019

Because offshore structures are affected by various environmental loads, the risk of damage is high. As a result of ever-changing ocean environmental loads, damage to offshore structures is expected to differ from year to year. However, in previous studies, it was assumed that a relatively short period of load acts repeatedly during the design life of a structure. In this study, the residual life of an offshore wind turbine support structure was evaluated in consideration of the timing uncertainty of the ocean environmental load. Sampling points for the wind velocity, wave height, and wave period were generated using a central composites design, and a transfer function was constructed from the numerical analysis results. A simulation was performed using the joint probability model of ocean environmental loads. The stress time history was calculated by entering the load samples generated by the simulation into the transfer function. The damage to the structure was calculated using the rain-flow counting method, Goodman equation, Miner's rule, and S-N curve. The results confirmed that the wind speed generated at a specific time could not represent the wind speed that could occur during the design life of the structure.