• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.295-305
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• 2023

This study introduces a smoothed finite-element implementation into the phase-field framework. In recent years, the phase-field method has recieved considerable attention in crack initiation and propagation since the method needs no further treatment to express the crack growth path. In the phase-field method, high strain-energy accuracy is needed to capture the complex crack growth path; thus, it is obtained in the framework of the smoothed finite-element method. The salient feature of the smoothed finite-element method is that the finite element cells are divided into sub-cells and each sub-cell is rebuilt as a smoothing domain where smoothed strain energy is calculated. An adaptive quadtree refinement is also employed in the present framework to avoid the computational burden. Numerical experiments are performed to investigate the performance of the proposed approach, compared with that of the finite-element method and the reference solutions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.1
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• pp.17-26
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• 2014

This paper presents a dynamic crack propagation algorithm based on the Moving Least Squares(MLS) difference method. The derivative approximation for the MLS difference method is derived by Taylor expansion and moving least squares procedure. The method can analyze dynamic crack problems using only node model, which is completely free from the constraint of grid or mesh structure. The dynamic equilibrium equation is integrated by the Newmark method. When a crack propagates, the MLS difference method does not need the reconstruction of mode model at every time step, instead, partial revision of nodal arrangement near the new crack tip is carried out. A crack is modeled by the visibility criterion and dynamic energy release rate is evaluated to decide the onset of crack growth together with the corresponding growth angle. Mode I and mixed mode crack propagation problems are numerically simulated and the accuracy and stability of the proposed algorithm are successfully verified through the comparison with the analytical solutions and the Element-Free Galerkin method results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.658-661
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• 2010

본 논문에서는 교량의 볼트 체결부, 응력집중부 등 손상의 발생이 유력한 위치에 부착된 압전센서-무선 임피던스 센서노드를 통해 구조물의 건전성을 지속적으로 모니터링 하는 시스템을 소개하였다. 임피던스 기반 건전성 모니터링에 있어서 구조물에 발생하는 손상에 따라 민감하게 반응하는 주파수 성분이 달라지기 때문에, 이러한 주파수 영역을 자동으로 결정함과 동시에 손상에 관한 정보를 획득하기 위하여 인공신경망 기법을 적용하였다. 제안된 기법은 기존에 구축되어 있는 데이터베이스를 기반으로 구조물에 발생한 손상의 종류 및 손상의 정도를 판단하는 것을 목적으로 한다. 무선 임피던스 센서노드-인공신경망 기반 손상탐색 통합 시스템은 실제 강교량에서 발생한 볼트풀림, 균열 등 국부적인 손상의 진단을 위하여 적용되었으며, 그 유효성을 입증하였다.

• Journal of the Korean Institute of Gas
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• v.4 no.4 s.12
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• pp.25-33
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• 2000

In recent years, the subject of remaining life assessment has drawn considerable attention in power plants, where various structural components typically operate at high temperature and pressure. Thus a life prediction methodology accounting for high temperature creep fracture is increasingly needed for the components. Critical defects in such structures are generally found in the form of semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. On this background, we first develop an auto mesh generation program for detailed 3-D finite element analyses of axial and circumferential semi-elliptical surface cracks in a piping system. A high temperature creep fracture parameter $C^{\ast}$-integral is obtained from the finite element analyses of generated 3-D models. Post crack growth module is further appended here to calculate the amount of crack growth. Finally the remaining lives of surface cracked pipes for various analytical parameters are assessed using the developed life assessment program.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.17-27
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• 1991

The determination of the stress intensity factors is investigated by means of a surface integral defined around the crack tip of the structure. It has been shown in this work that this integral is derived from the standard path integral J. The use of the surface integral has also been extended to the case where body forces act. Computer program obtaining the stress intensity factors $K_I$ and $K_{II}$ is developed, which prepares input variables from the result of the conventional finite element analysis. This paper provides a parabolic smooth curve function. By the use of the function and conventional element meshes in which the aspect ratio (element length/crack length)is about 25 percent, relatively correct $K_I$ and $K_{II}$ values can be obtained for the exterior radius ranging from 1/3 to 1 of the crack length.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.2
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• pp.101-108
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• 2021

To date, a number of stress intensity factor (SIF) solutions have been proposed for the cylindrical structure with circumferential through-wall cracks. However, each solution has a different format as well as applicable range. It is also known that there is a significant difference in predicted SIF values depending on the shape of the structure and the size of the crack. In this study, the applicability of various SIF solutions was analyzed by comparing the finite element analysis results for the case where a tensile load is applied to the cylindrical structure with circumferential through-wall crack. It is found that the calculated SIF gradually decreases and converges to a certain value with increasing length-to-radius ratio. Therefore, an appropriate length-to-radius ratio should be set in consideration of the dimensions of the actual cylindrical structure. For piping with sufficiently long cylinder, the ASME solution is found to be the most appropriate, and for a short cylinder, the API solution should be applied. On the other hand, the WEC solution requires careful attention to its application.

• Journal of the Korean Society of Groundwater Environment
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• v.6 no.3
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• pp.111-119
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• 1999

The purpose of this study is the simulation of discontinuous rockmass and identification of characteristics of discontinuity network as a branch of the study on characteristics of groundwater system in discontinuous rockmass for evaluation of safety on disposal site of radioactive waste. In this study the site for LPG underground storage was selected for the similarities of the conditions which were required for disposal site of radioactive waste. Through the identification of hydraulic properties. characteristics of discontinuities and selection of discontinuity model around LPG underground storage facility. the applications of discrete fracture network model were evaluated for the analysis of pathway. The orientation and spatial density of discontinuities are primarily important elements for the simulation of groundwater and solute transportation in discrete fracture network model. In this study three fracture sets identified and the spatial intensity (P$_{32}$) of discontinuities is revealed as 0.85 $m^2$/㎥. The conductive fracture intensity (P$_{32c}$) estimated for the simulation area around propane cavern (200${\times}$200${\times}$200) is 0.536 $m^2$/㎥. Truncated conductive fracture intensity (T-P$_{32c}$) is calculated as 0.26 $m^2$/㎥ by eliminating the fracture with the iowest transmissivity and based on this value the pathway from the water curtain to PC 2. PC 3 analyzed.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.33-39
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• 2024

Inspecting cracks to determine a structure's condition is crucial for accurate safety diagnosis. However, visual crack inspection methods can be subjective and are dependent on field conditions, thereby resulting in low reliability. To address this issue, this study automates the detection of concrete cracks in image data using ResNet, FPN, and the Mask R-CNN components as the backbone, neck, and head of a convolutional neural network. The performance of the proposed model is analyzed using the intersection over the union (IoU). The experimental dataset contained 1,203 images divided into training (70%), validation (20%), and testing (10%) sets. The model achieved an IoU value of 95.83% for testing, and there were no cases where the crack was not detected. These findings demonstrate that the proposed model realized highly accurate detection of concrete cracks in image data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.5
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• pp.823-833
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• 2001

In recent years, the subject of remaining life assessment has drawn considerable attention in chemical plants, where various structural components typically operate at high temperature an pressure. Thus a life prediction methodology accounting for high temperature creep fracture is increasingly needed for the components. Critical defects in such structures are generally found in the form of semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. On this background, we first develop an auto mesh generation program for detailed 3-D finite element analyses of axial and circumferential semi-elliptical surface cracks in a piping system. A high temperature creep fracture parameter C-integral is obtained from the finite element analyses of generated 3-D models. Post crack growth module is further appended here to calculate the amount of crack growth. Finally the remaining lives of surface cracked pipes for various analytical parameters are assessed using the developed life assessment program.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.245-249
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• 2005

The numerical simulation of a two-phase flow In a discrete fracture network model is presented in this paper, The purpose of this work is to consider density-driven flows induced by the density difference between hot autochthonous heavy brines and injected cold water. Mechanical consequences of high pressure waves on the fracture permeability and heat exchanges between fluids and rock matrix are neglected in this study. The finite volume method is employed to discretize spatially and the system is solved by using an IMPES(Implicit Pressure-Explicit Saturation) scheme. In order to solve the strong non-linearity of the system, the Newton-Raphson algorithm is used. The well-known Buckeley-Leverett problem is adapted to validate results calculated from the model and a relatively good agreement is obtained.