• Journal of computational fluids engineering
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• v.9 no.1
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• pp.1-9
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• 2004

Large eddy simulation is used to investigate the compressible flow over a cavity with high aspect ratio. The sub-grid scale stresses are modeled using the dynamic model. The compressible Navier-Stokes equations are solved with the sixth order accurate compact finite difference scheme in the space and the 4th order Runge-Kutta scheme in the time. The buffer Bone techniques are used for non-reflecting boundary conditions. The results show the shear layer oscillation over the cavity. The votical disturbances, the roll-up of vorticity, and impingement and scattering of vorticity at the downstream cavity edge can be seen in the shear layer. Several peaks for the resonant frequencies are found in the spectra of the vertical velocity at the center-line. The most energetic Peak near the downstream edge is different from that at the center part of the cavity The pressure has its minimum value in the vortex core inside the cavity, and becomes very high at the downstream face of the cavity. The variation of the model coefficient predicted by the dynamic model is quite large between 0 and 0.3. The model coefficient increases in the stream-wise evolution of the shear layer and sharply decreases near the wall due to the wall effect.

• Composites Research
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• v.16 no.4
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• pp.1-9
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• 2003

2 ply laminated composite is regarded to simulate the interply behavior of the belt layer of the tire. It was cone with 3 dimensional FE(Finite Element) analysis to determine interply shear stress and strain. Widthwise, the shear strain was measured by the pin method. These results are compared with those of CLT(classical lamination theory) in center region and those of Kassapoglou's and Kelsey's theory in edge region. In the FE analysis. rubber is assumed as linear elastic material. and rubber/cord laminate as the orthotropic material composed of cord and rubber In the FE result, interlaminar shear stress causing the interlaminar delamination has the largest value in the edge region of the inner rubber layer. Numerical results obtained coincides with CLT well in the center region, and agrees with other theoretical result little in the edge region.

• Wind and Structures
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• v.18 no.5
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• pp.511-528
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• 2014

The characteristics of wake galloping phenomenon for two parallel/unparallel circular cylinders were investigated via wind tunnel tests. The two cylinders were initially deployed in parallel and wake galloping phenomena were observed by varying the center-to-center distance. The effect of an unparallel arrangement of two cylinders was next investigated by fixing the spacing ratio of one side of the cylinders at 5.0D and the other side at 3.0D, in which D represents the diameter of the cylinder. For the unparallel disposition, the 5.0D side showed a small, limited vibration while the 3.0D side produced much larger amplitude of vibration, resulting in a rolling motion. However, the overall amplitude appeared to decrease in unparallel disposition when compared with the amplitude of the 3.0D - 3.0D parallel case. This represents the mitigation effect of wake galloping due to the unparallel disposition between two cylinders. Flow visualization tests with particle image velocimetry were conducted to identify flow fields between two cylinders. The test results demonstrate the existence of a complex interaction of the downstream cylinder with the shear layer generated by the upstream cylinder. When the spacing ratio was large enough, the shear layer was not observed and the downstream cylinder showed only limited random vibration.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.445-449
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• 2009

With the recent increase in the demand for the net-shape forming, numerical simulations are being commonly adopted to increase the efficiency and effectiveness of design of bulk metal forming processes. Proper consideration of tribological problems at the contact interface between the tool and workpiece is crucial in such simulations. In other words, lubrication and friction play important roles in metal forming by influencing the metal flow, forming load and die wear. In order to quantitatively estimate such friction condition or lubricant characteristic, the constant shear friction model is widely used for bulk deformation analyses. For this, new friction testing method based on the forward or backward extrusion process is proposed to predict the shear friction factor in this work. In this method, the tube-shaped punch pressurizes the workpiece so that the heights at the center and outer of punch (or mandrel) become different according to the friction condition. That is, the height at the center of punch is higher than that at the outer of the punch when the friction condition at the contact interface is severe. From this founding, the proposed friction testing method can be applied to effectively evaluate the friction condition in bulk metal forming processes.

• Steel and Composite Structures
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• v.12 no.1
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• pp.13-29
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• 2012

This paper is an experimental study on the behavior of vertical shear link in normal (steel section with and without stiffener) and composite (steel section with concrete located at the area limited to web and flanges of the section) configurations. This study is mainly aimed to perceive failure mechanism, collect laboratory data, and consider the effect of number of transverse reinforcements on strength and ductility of composite vertical links. There have been four specimens selected for examining the effects of different details. The first specimen was an I section with no stiffener, the second composed of I section with stiffeners provided according to AISC 2005. The third and fourth specimens were composed of I sections with reinforced concrete located at the area between its flanges and web. The tests carried out were of quasi-static type and conducted on full scale specimens. Experimental findings show remarkable increase in shear capacity and ductility of the composite links as compared to the normal specimens.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.3
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• pp.1028-1039
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• 1996

This study was focused on the examination of the flame structure and the combustion characteristics of diffusion flame which was formed the turbulent shear flow of a double coaxial air jet system. The shear flow was formed by the difference velocity of surrounding air jet(U$\_$s/) and center air jet (U$\_$c/). So experimental condition was divided S-type flame (.lambda. > 1) and C-type flame (.lambda. < 1) by velocity ratio .lambda. (=U$\_$s//U$\_$c/). For examination of the flame structure and the combustion characteristics in diffusion flame, coherent structure was observed in flame by schlieren photograph method. We measured fluctuating temperature and ion current simultaneously and accomplished the statistical analysis of its. According to schlieren photograph, the flame was stabilized in the rim of the direction of lower velocity air jet, coherent eddy was produced and developed by higher velocity air jet. The statistical data of fluctuating temperature and ion current was indicated that reaction was dominated by higher velocity air jet. The mixing state of burnt gas and non-burnt gas was distributed the wide area at Z = 100 mm of C-type flame.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.4
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• pp.201-208
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• 2003

The Hybrid Wall System(HWS) building composed of center core reinforced concrete walls and exterior steel frame has open space around the center core walls. It is necessary to develop design methodologies for the HWS building that the coupled shear walls withstand the most of lateral load and expect the most energy dissipation at the coupling beams and at wall foots. Major factors considered in this paper are connection type of coupling beams and scale of story. The studies of the system are investigated in terms of shear force, overturning moment, maximum lateral displacement, story drift ratio, and dynamical characteristics under the action of vertical and lateral forces such as wind and seismic loads.

• Smart Structures and Systems
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• v.30 no.5
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• pp.447-462
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• 2022

The viscosity of a shear-thickening fluid damper (STFD) can increase dramatically when the STFD undergoes high-rate of excitation. Therefore, accurate numerical modelling of the STFD has been considered difficult due to this distinct feature. This study aims to develop a numerical model to accurately simulate the response of the STFD. First, a STFD is designed, fabricated, and installed in the laboratory. Then, performance tests are conducted in which sine waves with nine frequencies at three amplitude levels are adopted as the displacement excitations to the STFD. A novel numerical model which contains two parameter sets of the discrete Bouc-Wen model as well as two parameters for transiting the two parameter sets. Therefore, a total number of eighteen parameters need to be identified in the damper model. The symbiotic organisms search is applied to optimize the parameters. Numerical simulation results demonstrate that the proposed STFD model with transit parameter sets outperforms the conventional discrete Bouc-Wen model. The proposed STFD model can be applied to analyses of structures in which STFDs are installed in the future.

• Earthquakes and Structures
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• v.19 no.1
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• pp.59-77
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• 2020

The code static eccentricity model for elastic torsional design of structures has two critical shortcomings: (1) the negation of the inertial torsional moment at the center of mass (CM), particularly for torsionally-unbalanced (TU) building structures, and (2) the confusion caused by the discrepancy in the definition of the design eccentricity in codes and the resistance eccentricity commonly used by engineers such as in FEMA454. To overcome these shortcomings, using the resistance eccentricity model that can accommodate the inertial torsional moment at the CM, interactive relations between shear and torsion are proposed as follows: (1) elastic responses of structures at instants of peak edge-frame drifts are given as functions of resistance eccentricity, and (2) elastic hysteretic relationships between shear and torsion in forces and deformations are bounded by ellipsoids constructed using two adjacent dominant modes. Comparison of demands estimated using these two interactive relations with those from shake-table tests of two TU building structures (a 1:5-scale five-story reinforced concrete (RC) building model and a 1:12-scale 17-story RC building model) under the service level earthquake (SLE) show that these relations match experimental results of models reasonably well. Concepts proposed in this study enable engineers to not only visualize the overall picture of torsional behavior including the relationship between shear and torsion with the range of forces and deformations, but also pinpoint easily the information about critical responses of structures such as the maximum edge-frame drifts and the corresponding shear force and torsion moment with the eccentricity.

• Korean Chemical Engineering Research
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• v.56 no.3
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• pp.343-348
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• 2018

Each of the two polycarbonates (PC) of different molecular weights was blended with acrylonitrile-butadiene-styrene (ABS) under high-shear rate processing to afford PC/ABS. Sizes of ABS dispersed phases and mechanical properties of PC/ABS blends were investigated and high-shear rate processing of PC/ABS was carried out by changing screw speed and processing time. Prepared specimens were examined by scanning electron microscope (SEM) to observe morphology changes. Sizes of ABS dispersed phases in PC/ABS blends were observed to decrease gradually as screw speeds increased. Tensile strengths and elongations of specimens were investigated by universal testing method (UTM) to study the influence of molecular weight of PC exerting on PC/ABS blends. As a result, PC1/ABS blends (PC1: higher molecular weight PC) exhibited more strengthened properties than PC2/ABS (PC2: lower molecular weight PC). The tensile strength of PC1/ABS showed an increasing tendency when the screw speed increased, and the elongation did not show a significant decrease, but increased slightly with increasing shear time at a constant screw speed of 1000 rpm.