• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.130-138
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• 2007

A coupled variational equation for fluid-structure interaction (FSI) problems is derived from a steady state Navier-Stokes equation for incompressible Newtonian fluid and an equilibrium equation for geometrically nonlinear structures. For a fully coupled FSI formulation, between fluid and structures, a traction continuity condition is considered at interfaces where a no-slip condition is imposed. Under total Lagrange formulation in the structural domain, finite rotations are well described by using the second Piola-Kirchhoff stress and Green-Lagrange strain tensors. An adjoint shape design sensitivity analysis (DSA) method based on material derivative approach is applied to the FSI problem to develop a shape design optimization method. Demonstrating some numerical examples, the accuracy and efficiency of the developed DSA method is verified in comparison with finite difference sensitivity. Also, for the FSI problems, a shape design optimization is performed to obtain a maximal stiffness structure satisfying an allowable volume constraint.

• Structural Engineering and Mechanics
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• v.63 no.1
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• pp.23-35
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• 2017

A nonlinear static procedure considering work-energy principle and global failure mechanism to estimate base shears of reinforced concrete (RC) frame-type structures is presented. The relative energy equation comprising of elastic vibrational energy, plastic strain energy and seismic input energy is obtained. The input energy is modified with a factor depending on damping ratio and ductility, and the energy that contributes to damage is obtained. The plastic energy is decreased with a factor to consider the reduced hysteretic behavior of RC members. Given the pre-selected failure mechanism, the modified energy balance equality is written using various approximations for modification factors of input energy and plastic energy in scientific literature. External work done by the design lateral forces distributed to story levels in accordance with Turkish Seismic Design Code is calculated considering the target plastic drift. Equating the plastic energy obtained from energy balance to external work done by the equivalent inertia forces considering, a total of 16 energy-based base shears for each frame are derived considering different combinations of modification factors. Ductility related parameters of modification factors are determined from pushover analysis. Relative input energy of multi degree of freedom (MDOF) system is approximated by using the modal-energy-decomposition approach. Energy-based design base shears are compared with those obtained from nonlinear time history (NLTH) analysis using recorded accelerograms. It is found that some of the energy-based base shears are in reasonable agreement with the mean base shear obtained from NLTH analysis.

• Structural Engineering and Mechanics
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• v.17 no.3_4
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• pp.357-378
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• 2004

Nonlinear dynamic analysis of a reinforced concrete (RC) frame under earthquake loading is performed in this paper on the basis of a hysteretic moment-curvature relation. Unlike previous analytical moment-curvature relations which take into account the flexural deformation only with the perfect-bond assumption, by introducing an equivalent flexural stiffness, the proposed relation considers the rigid-body-motion due to anchorage slip at the fixed end, which accounts for more than 50% of the total deformation. The advantage of the proposed relation, compared with both the layered section approach and the multi-component model, may be the ease of its application to a complex structure composed of many elements and on the reduction in calculation time and memory space. Describing the structural response more exactly becomes possible through the use of curved unloading and reloading branches inferred from the stress-strain relation of steel and consideration of the pinching effect caused by axial force. Finally, the applicability of the proposed model to the nonlinear dynamic analysis of RC structures is established through correlation studies between analytical and experimental results.

• Structural Engineering and Mechanics
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• v.31 no.6
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• pp.625-638
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• 2009

Applications of membrane mechanisms are widely found in nano-devices and nano-sensor technologies nowadays. An alternative approach for large deflection analysis of the orthotropic, elliptic membranes - subject to gravitational, uniform pressures often found in nano-sensors - is described in this paper. The material properties of membranes are assumed to be orthogonally isotropic and linearly elastic, while the principal directions of elasticity are parallel to the coordinate axes. Formulating the potential energy functional of the orthotropic, elliptic membranes involves the strain energy that is attributed to inplane stress resultant and the potential energy due to applied pressures. In the solution method, Rayleigh-Ritz method can be used successfully to minimize the resulting total potential energy generated. The set of equilibrium equations was solved subsequently by Newton-Raphson. The unparalleled model formulation capable of analyzing the large deflections of both circular and elliptic membranes is verified by making numerical comparisons with existing results of circular membranes as well as finite element solutions. The results are found in excellent agreements at all cases. Then, the parametric investigations are given to delineate the impacts of the aspect ratios and orthotropic elasticity on large static tensions and deformations of the orthotropic, elliptic membranes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.195-200
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• 1984

In-plane tension fatigue tests(R=0.1) were carried out to investigate the initiation and growth behaviors of very small surface fatigue cracks on smooth unnotched surfaces of type 304 stainless steel at room temperature. The present paper deals with the unification of two approaches to the analysis of fatigue: the one approach is based on fracture mechanics concept and the other on low-cycle fatigue concept. The results are;(1)Maximum crack length, 2 $a_{max}$, initiated at a very small surface scratch not exceeding 20 .mu.m which can exist on the surface after buffing. And the density of small surface crack is remarkably low compared to that of mild steel. (2) The growth rate, d(2a)/dN, of very small fatigue cracks can be represented by one straight line as a function of either stress intensity factor range, .DELTA. $K_{I}$ or cyclic total strain intensity factor range, .DELTA. $K_{\epsilon}$$_{I}$/, for various values of the nominal stress range.e.e.e.e.

• Journal of Microbiology and Biotechnology
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• v.23 no.6
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• pp.750-758
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• 2013

Anthrax is a bacterial disease caused by the aerobic spore-forming bacterium Bacillus anthracis, which is an important pathogen owing to its ability to be used as a terror agent. B. anthracis spores can escape phagocytosis and initiate the germination process even in antimicrobial conditions, such as oxidative stress. To analyze the oxidative stress response in B. anthracis and thereby learn how to prevent antimicrobial resistance, we performed protein expression profiling of B. anthracis strain HY1 treated with 0.3 mM hydrogen peroxide using a comparative proteomics-based approach. The results showed a total of 60 differentially expressed proteins; among them, 17 showed differences in expression over time. We observed time-dependent changes in the production of metabolic and repair/protection signaling proteins. These results will be useful for uncovering the metabolic pathways and protection mechanisms of the oxidative response in B. anthracis.

• Transactions of Materials Processing
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• v.16 no.8
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• pp.590-595
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• 2007

This paper introduces a new approach to take account of bending history in finite element inverse analysis during sheet metal forming process. A modified membrane element was adopted for finite element inverse analysis so that bending-unbending energy was additionally imposed in the total plastic energy, predicting bending-unbending regions using the geometry of the final shape and tools. An algorithm was applied to a cylindrical cup deep drawing process. The blank shape and the distribution of the thickness strain were compared with those obtained from the incremental finite element analysis in order to evaluate the effect of the bending history. The algorithm reduced the difference between the results of the inverse analysis from those of the incremental analysis due to bending history. The analysis was also carried out with the variation of the thickness of the initial blank to investigate the effect of bending deformation. The results showed that the difference was remarkably reduced as the thickness of the initial blank increased. This indicates that the finite element inverse analysis cooperated with the suggested scheme is useful to obtain more accurate results, especially when bending effects are significant.

• Steel and Composite Structures
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• v.27 no.6
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• pp.747-759
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• 2018

This study proposed a new type of concrete column that was confined with both steel angles and spiral hoops, named angle-steel and spiral confined concrete (ASCC) column. A total of 22 ASCC stub columns were tested under axial compression to investigate their behavior. For a comparison, three angle-steel reinforced concrete (ARC) stub columns were also tested. The test results indicated that ASCC column had a superior mechanical performance. The strength, ductility and energy absorption were considerably increased due to the improvement of confinement from spiral hoops. The confinement behavior and failure mechanism of ASCC column were investigated by the analysis of failure mode, load-deformation curve and section-strain distribution. Parametric studies were carried out to examine the influences of different parameters on the axial compression behavior of ASCC columns. A calculation approach was developed to predict the ultimate load carrying capacity of ASCC columns under axial compression. It was validated that the predicted results were in well agreement with the experimental results.

• Structural Engineering and Mechanics
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• v.40 no.2
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• pp.257-277
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• 2011

In this paper the geometrically nonlinear continuum plate finite element model, hitherto not reported in the literature, is developed using the total Lagrange formulation. With the layerwise displacement field of Reddy, nonlinear Green-Lagrange small strain large displacements relations (in the von Karman sense) and linear elastic orthotropic material properties for each lamina, the 3D elasticity equations are reduced to 2D problem and the nonlinear equilibrium integral form is obtained. By performing the linearization on nonlinear integral form and then the discretization on linearized integral form, tangent stiffness matrix is obtained with less manipulation and in more consistent form, compared to the one obtained using laminated element approach. Symmetric tangent stiffness matrixes, together with internal force vector are then utilized in Newton Raphson's method for the numerical solution of nonlinear incremental finite element equilibrium equations. Despite of its complex layer dependent numerical nature, the present model has no shear locking problems, compared to ESL (Equivalent Single Layer) models, or aspect ratio problems, as the 3D finite element may have when analyzing thin plate behavior. The originally coded MATLAB computer program for the finite element solution is used to verify the accuracy of the numerical model, by calculating nonlinear response of plates with different mechanical properties, which are isotropic, orthotropic and anisotropic (cross ply and angle ply), different plate thickness, different boundary conditions and different load direction (unloading/loading). The obtained results are compared with available results from the literature and the linear solutions from the author's previous papers.

• Journal of Microbiology and Biotechnology
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• v.34 no.3
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• pp.589-595
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• 2024

Latilactobacillus curvatus BYB3 (BYB3) is a species of lactic acid bacteria, formerly named Lactobacillus curvatus, which is isolated from kimchi. In this study, the effect of BYB3, Lactobacillus rhamnosus GG, and Lactobacillus acidophilus GP1B strain extracts at various concentrations was examined on B16F10, a mouse melanoma cell line. Cell viability was examined via MTT assay, and the results indicated that compared to the other two probiotics, BYB3 significantly decreased the total percentages of viable cells. The effects of BYB3 on cell migration and proliferation in B16F10 cells were evaluated using wound healing mobility and proliferation assays, respectively; the results indicated that BYB3 inhibits cell migration and proliferation in a concentration-dependent manner. Using human dermal fibroblast cells to investigate BYB3 extract in vivo had no effect on skin-related cells. Nonetheless, the BYB3 extract inhibited tumor growth in a mouse model, as demonstrated by liver slices. Therefore, this suggests that using BYB3 extract to inhibit melanoma may be a novel approach.