• Journal of Korea Water Resources Association
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• v.50 no.5
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• pp.325-334
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• 2017

In this study, the numerical investigation of the non-linear behavior of the fluid flow with physical properties, such as porosity and intrinsic permeability of a porous medium, and kinematic viscosity of a fluid, are carried out. The applied numerical model is ANSYS CFX which is the three-dimensional fluid dynamics model and this model is verified through the application of existing physical and numerical results. As a result of the verification, the results of the pressure gradient-velocity relationship and the friction coefficient-Reynolds number relationship produced from this study show relatively good agreement with those from existing physical and numerical experiments. As a result of the simulation by changing the porosity and intrinsic permeability of a porous medium and the kinematic viscosity of a fluid, the kinematic viscosity has the biggest effect on the non-linear behavior of the fluid flow in the porous medium.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.718-725
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• 2002

A wall type friction damper is newly Proposed in this paper to improve the performance of R/C framed structures under earthquake loads. Although traditional dampers are usually placed as bracing members, the application ot bracing-type dampers into R/C structures is not as simple as those of steel structures due to the connection between R/C members and dampers and the stress concentration in connection region. Proposed damper is consisted of Teflon-sheet slider and R/C shear wall. The damper can also avoid stress concentration and reduce P-Δ effect. To evaluate the performance of proposed damper, nonlinear dynamic analyses are carried on 10 story and 3 bay R/C structures with numerical model for the damper. It is shown that the damper reduces the inter-story drifts and the time-historic responses; especially the damper prevents from forming plastic hinges on the lower columns.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.973-978
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• 2010

In this paper, we studied the shimmy phenomena of an aircraft nose landing gear considering free-play. Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. This phenomena is caused by a couple of conditions such as low torsional stiffness of the strut, friction and free-play in the gear, wheel imbalance, or worn parts, and it may make an aircraft unstable. Free-play non-linearity is linearized by the described function for a stability analysis in a frequency domain, and time marching is performed using the fourth-order Runge-Kutta method. We performed the numerical simulation of the nose landing gear shimmy and investigated its linear and nonlinear characteristics. From the numerical results, we found limit-cycle-oscillations at the speed under linear shimmy speed for the case considering free-play and it can be concluded that the shimmy stability can be decreased by free-play.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.489-494
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• 2013

This study aims to understand the mode characteristics of a droplet under a periodic forced vibration. To predict the resonance frequency of a droplet, theoretical and experimental approaches were employed. A high-speed camera was used to capture the various deformation characteristics of a droplet-mode shape, detachment, separated secondary droplet, and skewed deformation. The comparison between the theoretical and the experimental approaches shows a ~10% discrepancy in the prediction of the resonance frequency, which appears to be caused by the effect of contact line friction, nonlinear wall adhesion, and experimental uncertainty. Owing to contact-line pinning and smaller amplitude, the droplet shape becomes symmetric and the size of each lobe at the resonance frequency exceeds that at the neighbor, which is out of resonance.

• Ocean Systems Engineering
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• v.3 no.4
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• pp.257-273
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• 2013

Top tensioned riser (TTR) is often used in a floating oil/gas production system deployed in deep water for oil/gas transport. This study focuses on the extension of the existing numerical code, known as CABLE3D, to allow for static and dynamic simulation of a TTR connected to a floating structure through a tensioner system or buoyancy can, and restrained by riser guides at different elevations. A tensioner system usually consists of three to six cylindrical tensioners. Although the stiffness of individual tensioner is assumed to be linear, the resultant stiffness of a tensioner system may be nonlinear. The vertical friction between a TTR and the hull at its riser guide is neglected assuming rollers are installed there. Near the water surface, a TTR is forced to move horizontally due to the motion of the upper deck of a floating structure as well as related riser guides. The extended CABLE3D is then integrated into a numerical code, known as COUPLE, for the simulation of the dynamic interaction among the hull of a floating structure, such as spar or TLP, its mooring system and riser system under the impact of wind, current and waves. To demonstrate the application of the extended CABLE3D and its integration with COUPLE, the numerical simulation is made for a truss spar under the impact of Hurricane "Ike". The mooring system of the spar consists of nine mooring lines and the riser system consists of six TTRs and two steel catenary risers (SCRs).

• Advances in concrete construction
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• v.10 no.4
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• pp.357-367
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• 2020

The impulse of this paper is to examine the influence of unsteady flow comprising of Eyring-Powell nanofluid over a stretched surface. This work aims to explore efficient transfer of heat in Eyring-Powell nanofluid with bio-convection. Nanofluids possess significant features that have aroused various investigators because of their utilization in industrial and nanotechnology. The influence of including motile microorganism is to stabilize the nanoparticle suspensions develop by the mixed influence of magnetic field and buoyancy force. This research paper reveals the detailed information about the linearly compressed Magnetohydrodynamics boundary layer flux of two dimensional Eyring-Powell nanofluid through disposed surface area due to the existence of microorganism with inclusion the influence of non- linear thermal radiation, energy activation and bio-convection. The liquid is likely to allow conduction and thickness of the liquid is supposed to show variation exponentially. By using appropriate similarity type transforms, the nonlinear PDE's are converted into dimensionless ODE's. The results of ODE's are finally concluded by employing (HAM) Homotopy Analysis approach. The influence of relevant parameters on concentration, temperature, velocity and motile microorganism density are studied by the use of graphs and tables. We acquire skin friction, local Nusselt and motil microorganism number for various parameters.

• Magazine of the Korea Concrete Institute
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• v.8 no.4
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• pp.201-211
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• 1996

It is expected that recent development of the mechanical model will replace previous empirical methods of detailing. In this study, a mechanical model is proposed to analyze the behavior of the anchorage zone of prestressed concrete members. Main characteristics of the proposed model lies on its rational consideration of material properties, and concrete strength in biaxial stress state and that of local zone reinforced by spirals. Shear friction strength of concrete surrounding spirals are also considered. The results of' the proposed method as well as the known Strut-and-Tie method and nonlinear finite element analysis are compared with some typical experimental results. We get good agreement to the failure mode as well as the failure load from test results. And it can be shown that three dimentional failure mechanism, which cannot be expected by the method based on 2D analysis, can be explained by proposed model.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.4
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• pp.38-46
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• 1999

This paper discusses the repetitive tracking control method for a coarse-fine actuator. The proposed system is composed of a magnetic linear drive as a coarse actuator and a piezoelectric linear positioner as a fine actuator. In particular, nonlinear friction in a magnetic linear drive and hysteresis characteristic of a piezoelectric linear positioner are modeled first. The feedback linearization loop uses these models in tracking position control. The control strategy is then further extended to include a repetitive control algorithm in tracking periodic reference inputs. This repetitive controller is implemented on the existing PID controller augmented with feedback linearization loop. The experimental results show that performance in tracking sinusoidal waveforms is noticeably improved by augmenting a PID controller with feedback linearization loop and a repetitive controller together.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1337-1347
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• 2013

The parametric analysis on ultimate behavior of buried cylindrical GFRP(Glass Fiber Reinforced Polymer) septic tank was presented. Two kinds of F.E. analysis model(soil-spring model and 3D full model) was constructed. The ultimate behavior of septic tank was investigated according to the size of stiffened steel ring and properties of underground soil. Ramberg-Osgood model and Druker-Prager model were used for material nonlinear characteristics of GFRP septic tank and soil, respectively. The diameter and thickness of stiffened steel ring inside septic tank, elastic modulus and internal friction angle of soil were selected for parametric variables. The ultimate behavior of septic tank, load-displacement, axial and hoop strain, were calculated and investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.1045-1052
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• 2015

In this paper, a stabilized control algorithm for the large rotating stand of a long-range surveillance radar (LRSR) system is introduced. The stabilized control algorithm for this large rotating stand system was designed using mathematical plant modeling. The LRSR system is located on high ground and has a wide surface, making it susceptible to the effects of wind, which increases the bearing friction and reduces the stability of the rotating stand. The disturbance caused by the wind was analyzed using computational fluid dynamics (CFD) in this study. The results of the CFD analysis were used to construct a control algorithm for the disturbance . The performance of the proposed control algorithm was demonstrated experimentally and through simulations. The plant model and the control algorithm were constructed in Matlab/Simulink.