• Structural Engineering and Mechanics
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• v.50 no.1
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• pp.19-36
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• 2014

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.185-190
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• 2007

In this study, we developed the 2.5D EM modeling and inversion algorithm for cross-hole source and receiver geometry. Considering the cross-hole environment, we use a VMD (vertical magnetic dipole) as a source and vertical magnetic fields as a measuring data. Developed inversion algorithm is tested for the isolated block model which has a conductive and a resistivity anomaly respectively. For the conductive anomaly, its size and resistivity are inverted well on the inversion results, while for the resistive anomaly, the location of anomalous block is shown on the inverted section, but its values are far from the exact value. Furthermore, artificial conductive anomalies are shown around the resistive anomalous zone. If we consider the inversion artifact shown in the test inversion of restive block, it is almost impossible to image the resistive zone. However, the main target of EM tomography in the engineering problem is conductive target such as fault zone, and contaminated zone etc., EM tomography algorithm can be used for detecting the anomalous zone.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.649-659
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• 2002

For a variety of elastic-plastic stress fields of plane strain specimens, many research works verified the validity of J-T approach. To generalize the validity of J-T method, however, further investigations are needed for more practical 3D structures than the idealized geometries as plane strain specimens. In this work, selecting two main types of structures such as plate and straight pipe, we perform 3D finite element(FE) modeling, and accompanying elastic, elastic-plastic FE analyses. We then study the validity of J-T application to 3D structures, and present some useful informations for the design or assessment of pipe welds by comparing the stress fields from the detailed 3D FE analyses to those predicted with J-T two parameters.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.3-17
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• 2007

This paper provides an introduction to life-span simulation and numerical approach to support the performance design processes of reinforced concrete structures. An integrated computational system is proposed for life-span simulation of reinforced concrete. Conservation of moisture, carbon dioxide, oxygen, chloride, calcium and momentum is solved with hydration, carbonation, corrosion, ion dissolution. damage evolution and their thermodynamic/mechanical equilibrium. Coupled analysis of mass transport and damage mechanics associated with steel corrosion is presented for structural performance assessment of reinforced concrete. Multi-scale modeling of micro-pore formation and transport phenomena of moisture and ions are mutually linked for predicting the corrosion of reinforcement and volumetric changes. The interaction of crack propagation with corroded gel migration can also be simulated. Two finite element codes. multi-chemo physical simulation code (DuCOM) and nonlinear dynamic code of structural reinforced concrete (COM3) were combined together to form the integrated simulation system. This computational system was verified by the laboratory scale and large scale experiments of damaged reinforced concrete members under static loads, and has been applied to safety and serviceability assessment of existing structures. Based on the damage details predicted by the nonlinear finite element analytical system, the life-span-cost of RC structures including the original construction costs and the repairing costs for possible damage during the service life can be evaluated for design purpose.

• Journal of Magnetics
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• v.16 no.2
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• pp.181-185
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• 2011

To improve trapped field characteristics of a high temperature superconducting (HTS) bulk, a technique to implement artificial holes has been studied. The artificial holes, filled up with epoxy or metal, may provide better cooling channel and enhance mechanical strength of the HTS bulk. Although many useful researches based on experiments have been reported, a numerical approach is still limited because of several reasons that include: 1) highly non-linear electromagnetic properties of HTS; and 2) difficulty in modeling of randomly scattered "small" artificial holes. In this paper, a 2-D finite element method with iteration is adopted to analyze trapped field characteristics of HTS bulk with artificial holes. The validity of the calculation is verified by comparison between measurement and calculation of a trapped field in a $40{\times}40\;mm$ square and 3.1 mm thick HTS bulk having 16 artificial holes with diameter of 0.7 mm. The effects of sizes and array patterns of artificial holes on distribution of trapped field within HTS bulk are numerically investigated using suggested method.

• Journal of Welding and Joining
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• v.29 no.5
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• pp.63-71
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• 2011

Three-dimensional finite element analysis is performed to study the temperature distribution phenomenon of TIG assisted friction stir welding (TAFSW) between dissimilar plates (Al 6061-T6 and stainless steel 304). TAFSW is a solid-state welding process that integrates TIG (Tungsten Inert Gas) into a friction stir welding (FSW), to preheat the harder material ahead of FSW tool during welding. In order to facilitate the industrial application of welding, 3D numerical modeling of heat transfer has been carried out applying Finite Element Method (FEM). The temperature distribution due to heat generation during TAFSW on dissimilar materials joint is analysed using in-house solver. Moving heat source along with frictional heat between the work specimens and tool surface is considered to calculate the heat input. The analytical model used predicts successfully the maximum welding temperatures that occur on the dissimilar materials during TAFSW. Comparison with the infra red camera and thermocouple measurement results shows that the results from the current numerical simulation have good agreement with the measured data.

• Journal of Korean Society of Steel Construction
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• v.11 no.2 s.39
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• pp.181-190
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• 1999

The objective of this study is to investigate the structural behavior of the composite slabs with the new-shaped deckplate. In order to examine the deckplate as structural members, the composite slabs with new-shaped deckplate are compared and verified with the international design codes, and the simple inertia-moment equation of the composite slabs is suggested from the regression analysis of the results of the experiments. Besides, the finite element analysis was added on the purpose of the observation of structural behavior of the section items such as the Locking rib and the Dovetail. 36 experiments of composite slabs were performed with two new-type deckplates. And the finite-element analysis was performed by ABAQUS package with the function of the 3-dimension solid modeling.

• Elastomers and Composites
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• v.44 no.4
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• pp.378-383
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• 2009

In this study, the use of 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. In order to improve the accuracy of forming analysis, more precise modeling of core shape and consideration of work-hardening of previous core forming are carried out. 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 post-buckling behavior.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.411-416
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• 2008

A strength problem of propeller blades for large container ships at astern condition has been occasionally reported due to the application of a highly skewed propeller which can reduce the hull surface fluctuation forces. A finite element analysis code for propeller blade was developed and utilized since 1985. Recently, however, further fine mesh modeling for finite element analysis is required to yield higher accuracy in the analysis. The present study shows an application of FE analysis code to the highly skewed propeller for large container ships. Results of FE analysis show that the number of FE mesh affects largely on strength, and also the calculated strength with fine mesh gives good agreements to those of other FEM codes. A method to enlarge strength near the trailing edge was introduced considering the strength criterion on the blade.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.263-268
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• 2003

This paper presents a result of performance evaluation fur non-contact scanning probe microscopy with respect to the vibration characteristics of cantilevers with tips. One of the current issues of the scanning probe microscopy technology is to increase the measurement speed, which is closely tied with the dynamic characteristics of cantilevers. The primary concern in this research is to investigate the relation between the maximum possible speed of non-contact scanning probe microscopy and the dynamic characteristics of cantilevers. First, the finite element analysis is made fur the vibration characteristics of various cantilevers in use. The computed natural frequencies of the cantilevers are in good agreement with measured ones. Then, each cantilever is tested with topographic measurement for a standard sample with the scanning speed changed. The performances of cantilevers are analyzed along with the natural frequencies of cantilevers. Experiments are also performed to test the effects of how to attach cantilevers in the piezo-electric actuator. Finally, measurement sensitivity has been analyzed to enhance the performance of scanning probe microscopy.