• Wind and Structures
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• v.30 no.4
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• pp.367-378
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• 2020

Two-dimensional Delayed Detached Eddy Simulation (DDES) was carried out to investigate the uniform flow over a twin-box bridge deck (TBBD) with various gap ratios of L/C=5.1%, 12.8%, 25.6%, 38.5%, 73.3% and 108.2% (L: the gap-width between two girders, C: the chord length of a single girder) at Reynolds number, Re=4×104. The aerodynamic coefficients of the prototype deck with gap ratio of 73.3% obtained from the present simulation were compared with the previous experimental and numerical data for different attack angles to validate the present numerical method. Particular attention is devoted to the fluctuating pressure distribution and forces, shear layer reattachment position, wake velocity and flow pattern in order to understand the effects of gap ratio on dynamic flow interaction with the twin-box bridge deck. The flow structure is sensitive to the gap, thus a change in L/C thus leads to single-side shedding regime at L/C≤25.6%, and co-shedding regime at L/C≥35.8% distinguished by drastic changes in flow structure and vortex shedding. The gap-ratio-dependent Strouhal number gradually increases from 0.12 to 0.27, though the domain frequencies of vortices shedding from two girders are identical. The mean and fluctuating pressure distributions is significantly influenced by the flow pattern, and thus the fluctuating lift force on two girders increases or decreases with increasing of L/C in the single-side shedding and co-shedding regime, respectively. In addition, the flow mechanisms for the variation in aerodynamic performance with respect to gap ratios are discussed in detail.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1053-1060
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• 2011

This study is performed to determine the drug concentration profiles of drug-eluting stents (DES) for an ideal circular ring stent and intertwined stent models for various Reynolds numbers (Re = 200, 400, and 800). The Navier.Stokes equations coupled with the advection-diffusion equation are solved numerically in order to determine how the flow patterns and drug deposition are affected in the in-stent and post-stent regions where flow separation and recirculation occur. The presence of DES within the arterial segment affects the local drug distribution in the flow field. As a result, the drug concentration for the intertwined stent is higher over the in-stent region in comparison with the ideal stents. For a given stent geometry, the local drug concentration in the in-stent region decreases with Reynolds number, while for a given Reynolds number, the local drug concentration is relatively insensitive to the stent geometry. The results show that drug concentration along the arterial wall is significantly higher within the in-stent and post-stent regions for the intertwined stent geometry than for the ideal stent geometries.

• Journal of the Korean Geotechnical Society
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• v.31 no.12
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• pp.59-69
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• 2015

This study examined the magnitude and distribution of earth pressure on the support system in a jointed rock mass due to the different joint sets as well as varying the rock type and joint condition (joint shear strength and joint inclination angle). Based on a physical model test and its numerical simulation, a series of numerical parametric analyses were conducted using a discrete element method. The results showed that the induced earth pressure was affected significantly by a joint set depending on the inclusion of the joint inclination angle, which induces a joint sliding condition, but the number of joint sets alone was not important, even though the earth pressure could be increased slightly as the number of joint sets is increased. In addition, the study results were compared with Peck's earth pressure for soil ground, which indicated that the earth pressure in a jointed rock mass could be considerably different from that in soil ground. The study suggests that the effects of joint sets as well as rock type and joint condition are important factors affecting the earth pressure in a jointed rock mass and they should be considered when designing a support system in a jointed rock mass.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.4
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• pp.1581-1588
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• 2011

In this study, flow characteristics in a multi-cavity injection molding process were investigated. One of main problems occurred in the multi-cavity molding is a flow imbalance among cavities since it affects physical properties and quality of products. Charge imbalance is caused by the uneven shear stress. Therefore, changes in viscosity affect the physical properties of resin and injection conditions differ in the filling imbalance phenomenon. Through, this study focus on experimental studies of flow imbalance for PC and PP resin occurring in a balanced delivery system. Experimental results were compared with CAE results. By experimental and CAE analysis, main cause for the flow imbalance is temperature distribution in cross section of runner. New runner system with a simple change of runner shape was suggested to avoid the flow imbalance. A series of simulation to confirm feasibility of Volume Runner's effects was conducted using injection molding CAE.

• Journal of the Korean institute of surface engineering
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• v.45 no.5
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• pp.181-187
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• 2012

The Friction Stir Welding (FSW) has mainly been used for making butt joints in Al alloys. The development of Friction Stir Lap Welding (FSLW) would expand the number of applications. In this study, microstructures and mechanical properties of FSLW in A5052 alloy were investigated under varying rotating speed and probe length. Investigating the characteristics as FSLWed conditions were as below ; Failure Maximum load by shear fracture was increased proportional to the width of joint area, which was increased by input heat, stirring intensity in the case of 2.3 mm probe length. Tensile fracture occurred, and maximum load was determined due to side worm hole of joint area and softening of microstructure in the case of 3.0 mm probe length. In the case of 3.7 mm probe length, material hook and bottom worm hole were appeared at the end interface of joint area. The most sound FSLW condition with no defects was 3.0 mm probe length and 1500 rpm-100 mm/min. No defects were showed in 1500 rpm-100 mm/min and 1800 rpm-100 mm/min, but Vickers microhardness distribution in TMAZ/HAZ which was fracture zone was lower in 1800 rpm-100 mm/min than in 1500 rpm-100 mm/min. In this condition highest tensile strength, 215 MPa (allowable rate 78% of joint efficient) was obtained.

• Structural Engineering and Mechanics
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• v.71 no.6
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• pp.627-641
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• 2019

The paper focuses on bending analysis of the functionally graded (FG) plates with arbitrary shapes and boundary conditions. The material property of FG plates is modelled by using the power law distribution. Based on the first order shear deformation plate theory (FSDT), the governing equations as well as boundary conditions are formulated and obtained by using the principle of virtual work. The coupled Boundary Element-Radial Basis Function (BE-RBF) method is established to solve the complex FG plates. The proposed methodology is developed by applying the concept of the analog equation method (AEM). According to the AEM, the original governing differential equations are replaced by three Poisson equations with fictitious sources under the same boundary conditions. Then, the fictitious sources are established by the application of a technique based on the boundary element method and approximated by using the radial basis functions. The solution of the actual problem is attained from the known integral representations of the potential problem. Therefore, the kernels of the boundary integral equations are conveniently evaluated and readily determined, so that the complex FG plates can be easily computed. The reliability of the proposed method is evaluated by comparing the present results with those from analytical solutions. The effects of the power index, the length to thickness ratio and the modulus ratio on the bending responses are investigated. Finally, many interesting features and results obtained from the analysis of the FG plates with arbitrary shapes and boundary conditions are demonstrated.

• Composites Research
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• v.31 no.6
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• pp.304-310
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• 2018

Autoclave process has been remaining as one of the most robust and stable process in fabricating structural composite part of aerospace industry. It has lots of advantages, however exhibits some disadvantages or limitations in capital investment and operation. Recently, there have been various Out-of-Autoclave process being researched and developed to overcome those limitations. In this study, laminate specimens were fabricated using LCM (Liquid Composite Molding) process, regarded as one of potential OoA process. DB (Double bagging), CAPRI (Controlled Atmospheric Pressure Resin Infusion), VAP (Vacuum Assisted Process) and Autoclave process were used for laminate specimens. Void content, Thickness, Tg (Glass Transition Temperature), ILSS (Interlaminar Shear Strength) and Flexural strength properties were evaluated for comparison. It is verified that Autoclave based specimen has uniform thickness distribution, the lowest void content and outstanding mechanical properties. And, CAPRI based specimen exhibits relatively good physical and mechanical properties over DB and VAP based specimen and comparable mechanical properties with autoclave based specimen.

• International journal of steel structures
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• v.18 no.4
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• pp.1440-1463
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• 2018

The Wagner coefficient is a key parameter used to describe the inelastic lateral-torsional buckling (LTB) behaviour of the I-beam, since even for a doubly-symmetric I-section with residual stress, it becomes a monosymmetric I-section due to the characteristics of the non-symmetrical distribution of plastic regions. However, so far no theoretical derivation on the energy equation and Wagner's coefficient have been presented due to the limitation of Vlasov's buckling theory. In order to simplify the nonlinear analysis and calculation, this paper presents a simplified mechanical model and an analytical solution for doubly-symmetric I-beams under pure bending, in which residual stresses and yielding are taken into account. According to the plate-beam theory proposed by the lead author, the energy equation for the inelastic LTB of an I-beam is derived in detail, using only the Euler-Bernoulli beam model and the Kirchhoff-plate model. In this derivation, the concept of the instantaneous shear centre is used and its position can be determined naturally by the condition that the coefficient of the cross-term in the strain energy should be zero; formulae for both the critical moment and the corresponding critical beam length are proposed based upon the analytical buckling equation. An analytical formula of the Wagner coefficient is obtained and the validity of Wagner hypothesis is reconfirmed. Finally, the accuracy of the analytical solution is verified by a FEM solution based upon a bi-modulus model of I-beams. It is found that the critical moments given by the analytical solution almost is identical to those given by Trahair's formulae, and hence the analytical solution can be used as a benchmark to verify the results obtained by other numerical algorithms for inelastic LTB behaviour.

• Earthquakes and Structures
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• v.20 no.1
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• pp.71-86
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• 2021

This paper focuses on the development and assessment of the expected damage for the rocking response of rigid anchored blocks, with irregular geometry and non-uniform mass distribution, considering the site conditions and the seismicity of Mexico City. The non-linear behavior of the restrainers is incorporated to evaluate the pure tension and tension-shear failure mechanisms. A probabilistic framework is performed covering a wide range of block sizes, slenderness ratios and eccentricities using physics-based ground motion simulation. In order to incorporate the uncertainties related to the propagation of far-field earthquakes with a significant contribution to the seismic hazard at study sites, it was simulated a set of scenarios using a stochastic summation methods of small-earthquakes records, considered as Empirical Green's Function (EGFs). As Engineering Demand Parameter (EDP), the absolute value of the maximum block rotation normalized by the body slenderness, as a function of the peak ground acceleration (PGA) is adopted. The results show that anchorages are more efficient for blocks with slenderness ratio between two and three, while slenderness above four provide a better stability when they are not restrained. Besides, there is a range of peak intensities where anchored blocks located in soft soils are less vulnerable with respect to those located in firm soils. The procedure used in here allows to take decisions about risk, reliability and resilience assessment of different types of contents, and it is easily adaptable to other seismic environments.

• Tunnel and Underground Space
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• v.31 no.1
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• pp.66-81
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• 2021

The effects of directional fracture tensor components and first invariant of fracture tensor on deformation moduli and shear moduli of fractured rock masses is analyzed based on regression analysis performed between 3-D fracture tensor parameters and deformability of DFN blocks. Using one or two deterministic joint sets, a total of 224 3-D discrete fracture network (DFN) cube blocks were generated with various configurations of deterministic density and probabilistic size distribution. The fracture tensor parameters were calculated for each generated DFN systems. Also, deformability moduli with respect to three perpendicular direction of the DFN cube blocks were estimated based on distinct element method. The larger the first invariant of fracture tensor, the smaller the values for the deformability moduli of the DFN blocks. These deformability properties present an asymptotic pattern above the certain threshold. It is found that power-law function describes the relationship between the directional deformability moduli and the corresponding fracture tensor components estimated in same direction.