• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.590-599
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• 2010

Recently, efficient operation and practical management of power plants have become important issues in the nuclear industry. In particular, typical aging parameters such as stress and cumulative usage factor should be determined accurately for continued operation of a nuclear power plant beyond design life. However, most of the major components have been designed via conservative codes based on a 2-D concept, which do not take into account exact boundary conditions and asymmetric geometries. The present paper aims to suggest an effective fatigue evaluation methodology that uses a prototype of the integrated model and its transfer functions. The validity of the integrated 3-D Finite Element (FE) model was proven by comparing the analysis results of individual FE models. Also, mechanical and thermal transfer functions, known as Green's functions, were developed for the integrated model with the standard step input. Finally, the stresses estimated from the transfer functions were compared with those obtained from detailed 3-D FE analyses results at critical locations of the major components. The usefulness of the proposed fatigue evaluation methodology can be maximized by combining it with an on-line monitoring system, and this combination, will enhance the continued operations of old nuclear power plants.

• Steel and Composite Structures
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• v.7 no.6
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• pp.487-502
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• 2007

In recent decades there has been a trend towards improved mechanical characteristics of materials used in footbridge construction. It has enabled engineers to design lighter, slender and more aesthetic structures. As a result of these construction trends, many footbridges have become more susceptible to vibrations when subjected to dynamic loads. In addition to this, some inherit modelling uncertainties related to a lack of information on the as-built structure, such as boundary conditions, material properties, and the effects of non-structural elements make difficult to evaluate modal properties of footbridges, analytically. For these purposes, modal testing of footbridges is used to rectify these problems after construction. This paper describes an arch type steel footbridge, its analytical modelling, modal testing and finite element model calibration. A modern steel footbridge which has arch type structural system and located on the Karadeniz coast road in Trabzon, Turkey is selected as an application. An analytical modal analysis is performed on the developed 3D finite element model of footbridge to provide the analytical frequencies and mode shapes. The field ambient vibration tests on the footbridge deck under natural excitation such as human walking and traffic loads are conducted. The output-only modal parameter identification is carried out by using the peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain, and dynamic characteristics such as natural frequencies mode shapes and damping ratios are determined. The finite element model of footbridge is calibrated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modelling parameters such as material properties. At the end of the study, maximum differences in the natural frequencies are reduced from 22% to only %5 and good agreement is found between analytical and experimental dynamic characteristics such as natural frequencies, mode shapes by model calibration.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.3
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• pp.123-137
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• 1998

The finite deformation with self contact problem of C. V. joint boots is analysed by using the implicit finite element code ABAQUS/Standard. It is shown that analysis results have a good agreement with experimental ones to the degree of maximum rotation angle. As an application of design modification, the effects of thickness change of the rounded part of boot model on the bending and the contact situation of deformed geometry are investigated. In this paper, the effect of the design modification in the end on the leakage is examined using 2-D finite element simulation. To solve the leakage problem of grease, the length of the small end is enlarged. From this study, it is confirmed that we can save the cost and time by applying FEM techniques to analyze and design the boot model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.443-444
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• 2011

This paper discusses a model order reduction for large order rotor dynamics systems results from the finite element discretization. Typical rotor systems consist of a rotor, built-on parts, and a support system, and require prudent consideration in their dynamic analysis models because they include unsymmetric stiffness, localized nonproportional damping and frequency dependent gyroscopic effects. When the finite element model has a very large number of degrees of freedom because of complex geometry, repeated dynamic analyses to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to finish within a practical design cycle. In this paper, the Krylov-based model order reduction via moment matching significantly speeds up the dynamic analyses necessary to check eigenvalues and critical speeds of a Nelson-Vaugh rotor system. With this approach the dynamic simulation is efficiently repeated via a reduced system by changing a running rotational speed because it can be preserved as a parameter in the process of model reduction. The Campbell diagram by the reduced system shows very good agreement with that of the original system. A 3-D finite element model of the Nelson-Vaugh rotor system is taken as a numerical example to demonstrate the advantages of this model reduction for rotor dynamic simulation.

• Transactions of Materials Processing
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• v.26 no.5
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• pp.286-292
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• 2017

Magnesium alloy shows strong anisotropy and asymmetric behavior in tension and compression curve, especially at room temperature. These characteristics limit the application of finite element method (FEM) which is based on conventional continuum mechanics. To accurately predict the material behavior of magnesium alloy at microstructural level, a methodology of fully coupled multiscale simulation is presented and a crystal plasticity model as a constitutive equation in the simulation of metal forming process is introduced in this study. The existing constitutive equation for rigid plastic FEM is modified to accommodate deviatoric stress component and its derivatives with respect to strain rate components. Viscoplastic self-consistent (VPSC) polycrystal model was selected as a constitutive model because it was regarded as the most robust model compared to Taylor model or Sachs model. Stiffness matrix and load vector were derived based on the new approach and implemented into $DEFORM^{TM}-3D$ via a user subroutine handling stiffness matrix at an elemental level. The application to extrusion and rolling process of pure magnesium is presented in this study to assess the validity of the proposed multiscale process.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.8
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• pp.205-212
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• 2003

In this study, in order to investigate a modeling technique of the structure with bolted joints, four kinds of finite element model are introduced; a solid bolt model, a coupled bolt model, a spider bolt model, and no bolt model. All proposed models take account on prestrained effect and contact behavior of flanges to be joined. Among these models, a solid bolt model, which is modeled by using a 3-D solid element and a surface-to-surface contact element between the head/nut and the flange interfaces, has the best accurate responses compared with the experimental results. In addition, coupled bolt model, which couples the degree of freedom between the head/nut and the flange, shows the best effectiveness and usefulness in view of computational time and memory usage. Finally, the bolt model proposed here is adopted for structural analysis of a large diesel engine of a ship consisting of several parts which is connected by long stay bolts.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.116-125
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• 2007

Human muscle skeletal model was developed for biomechanical study. The human model was consists with 19 bone-skeleton and 122 muscles. Muscle number of upper limb, trunk and lower limb part are 28, 60, 34 respectively. Bone was modeled with 3D beam element and muscle was modeled with spar element. For upper limb muscle modelling, rectus abdominis, trapezius, deltoideus, biceps brachii, triceps brachii muscle and other main muscles were considered. Lower limb muscle was modeled with gastrocenemius, gluteus maximus, gluteus medius and related muscles. The biomechanical stress and strain analysis of human was conducted by proposed finite element analysis model under Kumdo head hitting motion. In this study structural analysis has been performed in order to investigate the human body impact by Kumdo head hitting motion. As the results, the analytical displacement, stress and strain of human body are presented.

• Structural Engineering and Mechanics
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• v.10 no.6
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• pp.577-587
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• 2000

A 3D nonlinear finite element computation model is presented in order to analyze the concrete filled rectangular tubular (CFRT) composite structures. The concrete material model is based on a hypo-elastic orthotropic approach while the elasto-plastic hardening model is employed for steel element. The comparisons between experimental and analytical results show that the proposed model is a relatively simple and effective one. The analytical results show that the capacity of inner concrete of CFRT column mainly depends on the two diagonal zones, and the confining effect of CFRT section is mainly concentrated on the corner zones. At the ultimate state, the side concrete along the section cracks seriously, and the corner concrete softens with the increase of compressive strains until failure.

• Journal of Biomedical Engineering Research
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• v.29 no.3
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• pp.212-221
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• 2008

The total hip replacement (THR) has been used as the most effective way to restore the function of damaged hip joint. However, various factors have caused some side effects after the THR. Unfortunately, the success of the THR have been decided only by the proficiency of surgeons so far. Hence, It is necessary to find the way to minimize the side effect caused by those factors. The purpose of this study was to suggest the definite data, which can be used to design and choose the optimal hip implant. Using finite element analysis (FEA), the biomechanical condition of bone cement was evaluated. Stress patterns were analyzed in three conditions: cement mantle, procimal femur and stem-cement contact surface. Additionally, micro-motion was analyzed in the stem-cement contact surface. The 3-D femur model was reconstructed from 2-D computerized tomography (CT) images. Raw CT images were preprocessed by image processing technique (i.e. edge detection). In this study, automated edge detection system was created by MATLAB coding for effective and rapid image processing. The 3-D femur model was reconstructed based on anatomical parameters. The stem shape was designed using that parameters. The analysis of the finite element models was performed with the variation of parameters. The biomechanical influence of each parameter was analyzed and derived optimal parameters. Moreover, the results of FE A using commercial stem model (Zimmer's V erSys) were similar to the results of stem model that was used in this study. Through the study, the improved designs and optimal factors for clinical application were suggested. We expect that the results can suggest solutions to minimize various side effects.

• Coupled systems mechanics
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• v.12 no.5
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• pp.461-479
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• 2023

The paper deals with the finite element modelling of the free vibration and structural behavior of a particular four-floor reinforced concrete structure subjected to static equivalent seismic loads and supported by a shallow foundation system called SNSF (Spider Net System Footing). The two FE models are a simple 2D Matlab model and a detailed 3D model based on solid elastic elements using Altairworks (Hypermesh and Optistruct). Both models can simulate the soil structure interaction. We concentrate on the behavior of a representative cell involving two columns on five levels. The influence of the boundary conditions on the external vertical planes of the domain are duly studied. The Matlab model appears relevant for a primary estimation of frequencies and stiffness of the whole structure under vertical and lateral loads.