• Journal of Welding and Joining
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• v.35 no.2
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• pp.13-22
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• 2017

In laser full penetration welding process, full penetration hole(FPH) is formed as a result of force balance between the vapor pressure and the surface tension of the surrounding molten metal. In this work, a three-dimensional numerical model based on a conserved-mass level-set method is developed to simulate the transport phenomena during laser full penetration welding process, including full penetration keyhole dynamics. Ray trancing model is applied to simulate multi-reflection phenomena in the keyhole wall. The ghost fluid method and continuum method are used to deal with liquid/vapor interface and solid/liquid interface. The effects of processing parameters including laser power and scanning speed on the resultant full penetration hole diameter, laser energy distribution and energy absorption efficiency are studied. The model is validated against experimental results. The diameter of full penetration hole calculated by the simulation model agrees well with the coaxial images captured during laser welding of thin stainless steel plates. Numerical simulation results show that increase of laser power and decrease of welding speed can enlarge the full penetration hole, which decreases laser energy efficiency.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.105-115
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• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.355-365
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• 2000

As large underground projects such as radioactive waste disposal, hot water and heat storage, and geothermal energy become influential, the study, which consider all aspects of thermics, hydraulics and mechanics would be needed. Thermo-Hydro-Mechanical coupling analysis is one of the most complex numerical technique because it should be implemented with the combined three governing equations to analyze the behavior of rock mass. In this study, finite element code, which is based on Biot's consolidation theory, was developed to analyze the thermo-hydro-mechanical coupling in continuum rock mass. To verify the implemented program, one-dimensional consolidation model under the isothermal and non-isothermal conditions was analyzed and was compared with the analytic solution. The parametric study on two-dimensional consolidation was also performed and the effects of several factors such as poisson's ratio and hydraulic anisotropy on rock mass behavior were investigated. In the future, this program would be revised to be used for analysis of general discontinuous media with incorporating discrete joint model.

• Tunnel and Underground Space
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• v.12 no.3
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• pp.220-228
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• 2002

Thermal flow through jointed rock mass was analyzed by numerical methods. The effect of a single set of joints on the heat conduction was analyzed by one-dimensional model and compared with the analytical solution. When a joint is completely dry, the joint behaves as a thermal break inducing jumps in temperature distribution even at steady state. Therefore when joints are completely dry, individual joint has to be taken into consideration to get a good result. When joints are partially or fully saturated, the thermal conductivity of the joints increases drastically and the jumps in temperature distribution become less severe. Therefore the effect of joint in heat conduction can be well absorbed by continuum anisotropic model whose thermal properties represent overall thermal properties of the intact part and the discontinuities. Since the effect of joints becomes less important as the degree of the saturation increases, the overall thermal response of the rock mass also becomes close to isotropic. Therefore it can be concluded that a great effort has to be made to obtain a precise in-situ thermal properties in order to get a good prediction of the thermal response of a jointed rock mass.

• International Journal of Precision Engineering and Manufacturing
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• v.5 no.4
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• pp.50-60
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• 2004

A very flexible beam can be used to model various types of continuous mechanical parts such as cables and wires. In this paper, the dynamic properties of a very flexible beam, included in a multibody system, are analyzed using absolute nodal coordinates formulation, which is based on finite element procedures, and the general continuum mechanics theory to represent the elastic forces. In order to consider the dynamic interaction between a continuous large deformable beam and a rigid multibody system, a combined system equations of motion is derived by adopting absolute nodal coordinates and rigid body coordinates. Using the derived system equation, a computation method for the dynamic stress during flexible multibody simulation is presented based on Euler-Bernoulli beam theory, and its reliability is verified by a commercial program NASTRAN. This method is significant in that the structural and multibody dynamics models can be unified into one numerical system. In addition, to analyze a multibody system including a very flexible beam, formulations for the sliding joint between a very deformable beam and a rigid body are derived using a non-generalized coordinate, which has no inertia or forces associated with it. In particular, a very flexible catenary cable on which a multibody system moves along its length is presented as a numerical example.

• Advances in Computational Design
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• v.8 no.2
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• pp.97-112
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• 2023

The Finite Element (FE) modeling of Reinforced Concrete (RC) under seismic loading has a sensitive impact in terms of getting good contribution compared to experimental results. Several idealized model types for simulating the nonlinear response have been developed based on the plasticity distribution alone the model. The Continuum Models are the most used category of modeling, to understand the seismic behavior of structural elements in terms of their components, cracking patterns, hysteretic response, and failure mechanisms. However, the material modeling, contact and nonlinear analysis strategy are highly complex due to the joint operation of concrete and steel. This paper presents a numerical simulation of a chosen RC column under monotonic and cyclic loading using the FE Abaqus, to assessthe hysteretic response and failure mechanisms in the RC columns, where the perfect bonding option is used for the contact between concrete and steel. While results of the numerical study under cyclic loading compared to experimental tests might be unsuccessful due to the lack of bond-slip modeling. The monotonic loading shows a good estimation of the envelope response and deformation components. In addition, this work further demonstrates the advantage and efficiency of the damage distributions since the obtained damage distributions fit the expected results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.3
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• pp.255-280
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• 2024

If there are concerns about the stability of segment lining due to section deficiency or large deformation in shield TBM tunnel, reinforcement can be done through ground grouting outside the tunnel or by using steel plate reinforcement, ring beam reinforcement, or inner double layer lining inside the tunnel. Traditional analyses of shield TBM tunnels have been conducted using a continuum method that does not consider the segmented nature of segment lining. This study investigates the reinforcement mechanism for double layer reinforced sections with internal steel linings. By improving the modeling of segment lining, this study applies Break-joint mode (BJM), which considers the segmented characteristics of segment lining, to analyze the deformation characteristics of double layer reinforced sections. The results indicate that the existing concrete segment lining functioned similarly to ground reinforcement around the tunnel, rather than distribution the load. In general, both the BJM model considering the segmentation of segment lining and the continuum rigid method were similar deformation shapes and stress distributions of the lining under load. However, in terms of deformation, when the load strength exceeded the threshold, the deformation patterns of the two models differed.

• Advances in nano research
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• v.5 no.4
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• pp.303-311
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• 2017

The continuum elasticity model is applied to investigate quantitatively the growth features and nucleation mechanism of quantum dots, nanopits, and joint QDs-nanopits structures in GaInAlN quasyternary systems. We have shown that for GaInAlN material system at the critical strain of ${\varepsilon}^*=0.039$ the sign of critical energy and volume is changed. We assume that at ${\varepsilon}={\varepsilon}^*$ the mechanism of the nucleation is changed from the growth of quantum dots to the nucleation of nanopits. Obviously, at small misfit (${\varepsilon}$ < ${\varepsilon}^*$), the bulk nucleation mechanism dominates. However, at ${\varepsilon}$ > ${\varepsilon}^*$, when the energy barrier becomes negative as well as a larger misfit provides a low-barrier path for the formation of dislocations, the nucleation of pits becomes energetically preferable. The free energy of mixing for $Ga_{1-x-y}In_xAl_yN$ quasiternary system was calculated and studied and its 3D sketch was plotted.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.159-181
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• 2012

The segment lining which consists of segments and joints are main component of shield tunnel. There are a number of methods that are being used in design which compute the sectional forces of a ring of segment lining. The traditional design methods which do not consider the effect of joints have been commonly used for design procedure without a specific verification of structural analysis. This paper presents the result of a comparative study for analytical and numerical models of the shield tunnel segment lining. For the traditional methods, the elastic equation method and the Duddeck & Erdmann method were considered. The ring-beam and the continuum analysis model were also considered as the numerical model.

• The Journal of Engineering Geology
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• v.21 no.3
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• pp.221-230
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• 2011

The movement of rock cut slopes may result in upheaval of an adjacent road. Because most cut slopes consist of rock, road upheaval due to the movement of a cut slope is a rare phenomenon in Korea. We found that the movement of rock slopes which are heavily weathered and with strongly developed weak zones is governed by circular failure of the overall rock formation rather than by failure along discontinuities. The results of a numerical analysis revealed that the application of a ubiquitous joint model in a continuum analysis is appropriate for anisotropic rocks (e.g., schist) and for slopes for which the stability is influenced by a particular discontinuity. The results of a field investigation and numerical analyses suggest that retaining walls and anchors should be used to stabilize rock slopes and that real-time monitoring equipment should be installed to assess the reinforcing effect of the remedial measures.