• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3301-3303
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• 1999

A new method of measuring residual stresses in micromachined films using beam or ring structures is proposed. Using the proposed method, more exact value of residual stress can be obtained without any ambiguities in conventional buckling method. Theoretical modeling with respect to this method is described, and experiment is performed. The structure and fabrication process in this paper are simple and widely used in surface micromachining. Therefore, it is possible to obtain a synchronous measurement. A synchronous and reason -able estimation of residual stresses in micromachined films enables us to obtain the prediction of more exact performance in micromachined devices.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.560-563
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• 2008

A condensed model is proposed for the simulation of forming of sandwich sheet with pyramid core. A corresponding finite element analysis for L-type bending is carried out to prove the accuracy and the effectiveness. Simulation results are compared with those of experiment. Deformation shape and post-buckling behavior by simulation are in good agreement with those of experiment for the considerable range of deformation. From the comparison of force-displacement curve, it is shown that the proposed model shows good prediction of the forming force compared to the experiment. Thus, the effectiveness of the proposed method is sufficiently demonstrated.

• Journal of Ship and Ocean Technology
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• v.8 no.3
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• pp.40-49
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• 2004

Welding deformations injure the beauty of appearance of a structure, decrease its buckling strength and prevent increase of productivity. Welding deformations of real structures are complicated and the accurate prediction of welding deformations has been a difficult problem. This study proposes a method to predict the welding deformations of large structures accurately and practically based on the simplified thermal elasto-plastic analysis method. The proposed method combines the inherent strain theory with the numerical or theoretical analysis method and the experimental results. The weld joint is assumed to be divided into 3 regions such as inherent strain region, material softening region and base metal region. Characteristic material properties are used in structural modeling and analysis for reasonable simplification. Calculated results by this method show good agreement with the experimental results. It was proven that this method gives an accurate and efficient solution for the problem of welding deformation calculation of large structures.

• Earthquakes and Structures
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• v.24 no.2
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• pp.111-126
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• 2023

Highly reliable and versatile methods artificial intelligence (AI) have found multiple application in the different fields of science, engineering and health care system. In the present study, we aim to utilize AI method to investigated vibrations in the human leg bone. In this regard, the bone geometry is simplified as a thick cylindrical shell structure. The deep neural network (DNN) is selected for prediction of natural frequency and critical buckling load of the bone cylindrical model. Training of the network is conducted with results of the numerical solution of the governing equations of the bone structure. A suitable optimization algorithm is selected for minimizing the loss function of the DNN. Generalized differential quadrature method (GDQM), and Hamilton's principle are used for solving and obtaining the governing equations of the system. As well as this, in the results section, with the aid of AI some predictions for improving the behaviors of the various sport systems will be given in detail.

• Earthquakes and Structures
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• v.20 no.1
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• pp.109-122
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• 2021

Significant progress in the oil and gas industry advances the application of pipeline into an intelligent era, which poses rigorous requirements on pipeline safety, reliability, and maintainability, especially when crossing seismic zones. In general, strike-slip faults are prone to induce large deformation leading to local buckling and global rupture eventually. To evaluate the performance and safety of pipelines in this situation, numerical simulations are proved to be a relatively accurate and reliable technique based on the built-in physical models and advanced grid technology. However, the computational cost is prohibitive, so one has to wait for a long time to attain a calculation result for complex large-scale pipelines. In this manuscript, an efficient and accurate surrogate model based on machine learning is proposed for strain demand prediction of buried X80 pipelines subjected to strike-slip faults. Specifically, the support vector regression model serves as a surrogate model to learn the high-dimensional nonlinear relationship which maps multiple input variables, including pipe geometries, internal pressures, and strike-slip displacements, to output variables (namely tensile strains and compressive strains). The effectiveness and efficiency of the proposed method are validated by numerical studies considering different effects caused by structural sizes, internal pressure, and strike-slip movements.

• Structural Engineering and Mechanics
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• v.49 no.4
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• pp.427-448
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• 2014

At present, the time of easy oil and gas is over. Now, the largest part of fossil fuels is concentrated in the deepest levels of tectonic structures and in the sea shelves. One of the most cumbersome operations of their extraction is the bore-hole drilling. In connection with austere tectonic and climate conditions, their drivage every so often is associated with great and diversified technological difficulties causing emergencies on frequent occasions. As a rule, they are linked with drill string accidents. A key role in prediction of these situations should play methods of theoretical modelling. For this reason, there is a growing need for development and implementation of new numerical methods for computer simulation of critical and post-critical behavior of drill strings (DSs). In this paper, the processes of non-linear deforming of a DS in cylindrical cavity of a deep bore-hole are considered. On the basis of the theory of curvilinear flexible rods, non-linear constitutive differential equations are deduced. The effects of the longitudinal non-uniform preloading, action of torque and interaction between the DS and the bore-hole surface are taken into account. Owing to the use of curvilinear coordinates in the constraining cylindrical surface and a specially chosen concomitant reference frame, it became possible to separate the desired variables and to reduce the total order of the equation system. To solve it, the method of continuation the solution by parameter and the transfer matrix technique are applied. As a result of the completed numerical analysis, the critical states of the DS loading in the cylindrical channels of inclined bore-holes are found. It is shown that the modes of the post-critical deforming of the DS are associated with its irregular spiral curving prevailing in the zone of bottom-hole-assembly. The possibility of invariant state generation during post-critical deforming is established, condition of its bifurcation is formulated. It is shown that infinite variety of loads can correspond to one geometrical configuration of the DS. They differ each from other by contact force functions.

• Steel and Composite Structures
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• v.17 no.4
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• pp.497-516
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• 2014

The ultimate carrying capacity of axially loaded welded square box section members made of medium and high strength steels (nominal yield stresses varying from 345 MPa to 460 MPa), with large width-to-thickness ratios ranging from 35 to 70, is analyzed by finite element method (FEM). At the same time, the numerical results are compared with the predicted results using Direct Strength Method (DSM), modified DSM and Effective Yield Strength Method (EYSM). It shows that curve a, rather than curve b recommended in Code for design of steel structures GB50017-2003, should be used to check the local-overall interaction buckling strength of welded square section columns fabricated from medium and high strength steels when using DSM, modified DSM and EYSM. Despite all this, EYSM is conservative. Compared to EYSM and modified DSM, DSM provides a better prediction of the ultimate capacities of welded square box compression members with large width-thickness ratios over a wide range of width-thickness ratios, slenderness ratios and steel grades. However, for high strength steels (nominal yield strength greater than 460 MPa), the numerical and existent experimental results indicate that DSM overestimates the load-carrying capacities of the columns with width-thickness ratio smaller than 45 and slenderness ratio less than 80. Further, for the purpose of making it suitable for a wider scope, DSM has been modified (called proposed modified DSM). The proposed modified DSM is in excellent agreement with the numerical and existing experimental results.

• Steel and Composite Structures
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• v.27 no.5
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.1
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• pp.21-28
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• 2008

The CFT (Concrete Filled Steel Tube) columns became popular in high rise building construction due to not only its composite effect but also economic advantage. However, it has been pointed out in various previous researches that the current practice in CFT columns may lead the steel tube to probable local buckling at critical sections of the columns right after yielding. To resolve such a problem, the TR-CFT (Transversely Reinforced Concrete Filled Steel Tube) column is proposed to control or at least delay the local buckling state at the critical section by wrapping the CFT columns with carbon fiber sheet. The validity of the proposed column system is validated through the present paper by observing the experimental performance and comparing it with the analytical prediction of the TR-CFT columns with hish strength concrete. It is also shown that the current design code provisions such as ACI-318, in which the contribution of concrete confining effect filled in steel tube is not appropriately accounted for, may contain too much conservatism.

• Earthquakes and Structures
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• v.12 no.3
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• pp.321-332
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• 2017

The reverse fault is a dangerous geological hazard faced by buried steel pipelines. Permanent ground deformation along the fault trace will induce large compressive strain leading to buckling failure of the pipe. A hybrid pipe-shell element based numerical model programed by INP code supported by ABAQUS solver was proposed in this study to explore the strain performance of buried X80 steel pipeline under reverse fault displacement. Accuracy of the numerical model was validated by previous full scale experimental results. Based on this model, parametric analysis was conducted to study the effects of four main kinds of parameters, e.g., pipe parameters, fault parameters, load parameter and soil property parameters, on the strain demand. Based on 2340 peak strain results of various combinations of design parameters, a semi-empirical model for strain demand prediction of X80 pipeline at reverse fault crossings was proposed. In general, reverse faults encountered by pipelines are involved in 3D oblique reverse faults, which can be considered as a combination of reverse fault and strike-slip fault. So a compressive strain demand estimation procedure for X80 pipeline crossing oblique-reverse faults was proposed by combining the presented semi-empirical model and the previous one for compression strike-slip fault (Liu 2016). Accuracy and efficiency of this proposed method was validated by fifteen design cases faced by the Second West to East Gas pipeline. The proposed method can be directly applied to the strain based design of X80 steel pipeline crossing oblique-reverse faults, with much higher efficiency than common numerical models.