• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.2
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• pp.100-105
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• 1989

This paper presents an adaptive finite element method for magnetostatic force computation using Maxwell's stress tensor. Mesh refinements are performed automatically by interelement magnetic field intensity discontinuity errors and element force errors. In initial mesh, the computed forces for different integration paths give great differences, but converge to a certain value as mesh division is performed by the adaptive scheme, We obtained good agreement between analytic solutions and numerical values in typical examples.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.220-225
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• 2004

The mesh-insensitive structural stress procedure by Dong is modified to apply to the welded joints with local thickness variation and inignorable shear/normal stresses along local discontinuity surface. In order to make use of the structural stress based K solution for fatigue correlation of welded joints, a proper crack growth model needs to be developed. There exist some significant discrepancies in inferring the slope or crack growth exponent in the conventional Paris law regime. Two-stage crack growth model was not considered since its applications are focused upon the fatigue behavior in welded joints in which the load ratio effects are considered negligible. In this paper, a two-stage crack growth law considering high mean loading is proposed and proven to be effective in unifying the so-called anomalous short crack growth data.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.1
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• pp.246-254
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• 2001

The breech system can be considered as a pressure vessel with an internal plug under high explosive pressure. The system consists of a breech block(internal plug) whose front surface subjects to pressure, and a breech ring(pressure vessel). There is the geometric discontinuity around roots of connection parts and then stress concentration is introduced due to pressure, where contact effect may be ignored because contact plane between two equipments is parallel ideally, Generally high stress concentration phenomena shorten the life cycle of the mechanical system. It is well known that shock load is much more harmful on safety of the system than static load. In this present paper, several geometric design variables which may affect stress condition on the system are chosen and the parametric study on the design variables is carried using commercial FEM codes. Finally, the obtained results in the single lug breech system are applied to design the 3 lugs breech system. The 3 lugs breech system can reduce the maximum stress level.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.6
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• pp.605-611
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• 2007

A ship is composed of many grillage structures especially the deck which is consists of primary girders, transverse and longitudinal members. Several holes are arranged on these primary members for pipes, vents, etc. which cause stress concentration due to the discontinuity of the member. It is not easy to get the stress values around all these holes because of the huge amount of time necessary for computations. In this paper, a simple method to compute for the stress around the holes is suggested. This method is composed of two steps which are grillage analysis for primary members and detailed stress analysis using the results of the grillage analysis. This method is made for the design of the primary members with openings supporting the deck structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.321-327
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• 2007

This study presents a new gridless finite difference method for solving elastic crack problems. The method constructs the Taylor expansion based on the MLS(Moving Least Squares) method and effectively calculates the approximation and its derivatives without differentiation process. Since no connectivity between nodes is required, the modeling of discontinuity embedded in the domain is very convenient and discontinuity effect due to crack is naturally implemented in the construction of difference equations. Direct discretization of the governing partial differential equations makes solution process faster than other numerical schemes using numerical integration. Numerical results for mode I and II crack problems demonstrates that the proposed method accurately and efficiently evaluates the stress intensity factors.

• Coupled systems mechanics
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• v.11 no.1
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• pp.55-78
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• 2022

The main aim of this paper is the identification of the model parameters for the constitutive model of concrete and concrete-like materials capable of representing full set of 3D failure mechanisms under various stress states. Identification procedure is performed taking into account multi-scale character of concrete as a structural material. In that sense, macro-scale model is used as a model on which the identification procedure is based, while multi-scale model which assume strong coupling between coarse and fine scale is used for numerical simulation of experimental results. Since concrete possess a few clearly distinguished phases in process of deformation until failure, macro-scale model contains practically all important ingredients to include both bulk dissipation and surface dissipation. On the other side, multi-scale model consisted of an assembly micro-scale elements perfectly fitted into macro-scale elements domain describes localized failure through the implementation of embedded strong discontinuity. This corresponds to surface dissipation in macro-scale model which is described by practically the same approach. Identification procedure is divided into three completely separate stages to utilize the fact that all material parameters of macro-scale model have clear physical interpretation. In this way, computational cost is significantly reduced as solving three simpler identification steps in a batch form is much more efficient than the dealing with the full-scale problem. Since complexity of identification procedure primarily depends on the choice of either experimental or numerical setup, several numerical examples capable of representing both homogeneous and heterogeneous stress state are performed to illustrate performance of the proposed methodology.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.185-197
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• 2007

Limit analysis of upper and lower bound solutions has been well developed to provide the stability numbers for shallow tunnels in cohesive soil ($c_u$ material), cohesive-frictional soil (c'-$\phi$' material) and cohesionless soil ($\phi$'material). However, an extension of these methods to relatively deep circular tunnels in the cohesionless soil has been explored rarely to date. For this reason, the closed-form analytical solutions including lower bound solution based on the stress discontinuity concept and upper bound solution based on the kinematically admissible failure mechanism were proposed for assessing tunnel collapse load in this study. Consequently, the tunnel collapse load from those solutions was compared with both the finite element analysis and the previous analytical bound solutions and shown to be in good agreement with the FE results, in particular with the FE soil elements located on the horizontal tunnel axis.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.272-280
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• 2003

A definite shut-in pressure in hydraulic fracturing techniques is needed for obtaining the correct information on the in-situ stress regimes in rock masses. The relation between the behaviour of hydraulically induced fractures and the condition of remote stress is considered to be major reasons of an ambiguous shut-in pressure in hydraulic fracturing pressure-time history curves. This paper describes the results of a series of numerical analyses carried out using UDEC(Universal Distinct Element Code, Itasca), which is based on the discrete element method, to compare several methods for determining the shut-in pressure during hydraulic fracturing. The fully coupling of hydraulic and mechanical analysis was applied, and the effects of four different discontinuity geometries in numerical modelling have been investigated for this purpose. The effects of different remote stress regimes and different physical properties on hydraulic fracture propagation have been also analyzed. Several methods for obtaining shut-in pressure from the ambiguous shut-in curves have been applied to all the numerical models. The graphical intersection methods, such as (P vs. t) method, (P vs. log(t)) method, (log(P) vs. log(t)) method, give smaller values of the shut-in pressure than the statistical method, (dP/dt vs. P). Care should be taken in selecting a method for shut-in pressure, because there can be existed a stress anomaly around the wellbore and fracturing from the wellbore by a constant flow rate may have a more complicate mechanism.

• Geomechanics and Engineering
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• v.17 no.3
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• pp.295-305
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• 2019

The bedding plane has a significant influence on the effect of blasting fragmentation and the overall performance of underground mining. This paper explores the effects of fragmentation of the bedding plane and different angles by using the numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include a dynamic compressive and tensile failure which is applied to simulate the fractures generated by the explosion. Firstly, the cracks propagation with the non-bedding plane in the coal with two boreholes detonated simultaneously is calculated and the particle velocity and maximum principal stress at different points from the borehole are also discussed. Secondly, different delay times between the two boreholes are calculated to explore its effects on the propagation of the fractures. The results indicate that the coal around the right borehole is broken more fully and the range of the cracks propagation expanded with the delay time increases. The peak particle velocity decreases first and then increases with the distance from the right borehole increasing. Thirdly, different angles between the bedding plane and the centerline of the two boreholes and the transmission coefficient of stress wave at a bedding plane are considered. The results indicated that with the angles increase, the number of the fractures decreases while the transmission coefficient increases.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.868-880
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• 2020

One of the main concerns in the structural integrity of offshore pipelines is mechanical damage from external loads. Pipelines are exposed to fatigue failure in welded joints due to geometric discontinuity. In addition, fatigue loads such as currents, waves, and platform motions may cause significant plastic deformation and fracture or leakage within a relatively low-cycle regime. The 2007 ASME Div. 2 Code adopts the master S―N curve for the fatigue evaluation of welded joints based on the mesh-insensitive structural stress. An extension to the master S―N curve was introduced to evaluate the low-cycle fatigue strength. This structural strain method uses the tensile properties of the material. However, the monotonic tensile properties have limitations in describing the material behavior above the elastic range because most engineering materials exhibit hardening or softening behavior under cyclic loads. The goal of this study is to extend the cyclic stress-strain behavior to the structural strain method. To this end, structural strain-based procedure was established while considering the cyclic stress-strain behavior and compared to the structural strain method with monotonic tensile properties. Finally, the improved prediction method was validated using fatigue test data from full-scale girth-welded pipes.