• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.441-456
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• 2016

This work reports wave propagation in the nanocomposite cylinders that reinforced by straight single-walled carbon nanotubes based on a mesh-free method. Moving least square shape functions have been used for approximation of displacement field in weak form of motion equation. The straight carbon nanotubes (CNTs) are assumed to be oriented in specific or random directions or locally aggregated into some clusters. In this simulation, an axisymmetric model is used and also the volume fractions of the CNTs and clusters are assumed to be functionally graded along the thickness. So, material properties of the carbon nanotube reinforced composite cylinders are variable and estimated based on the Eshelby-Mori-Tanaka approach. The effects of orientation, aggregation and volume fractions of the functionally graded clusters and CNTs on dynamic behavior of nanocomposite cylinders are studied. This study results show that orientation and aggregation of CNTs have significant effects on the effective stiffness and dynamic behaviors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1950-1956
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• 1997

An engineering goal in vibration and noise professionals is to develope quiet machines at the preliminary design stage, and various numerical techniques such as FEM, SEA or BEM are one of the schemes toward the goal. In this paper, the research has been focused on the sensitivity effect of mesh sizes for FEM application so that the optimum size of the mesh that leads to engineering solution within acceptable computing time could be generated. In order to evaluate the mesh size effect, three important parameters have been examined : natural frequencies, number of modes and driving point mobility. First, several lower modes including the fundamental frequency of a 2-D plate structure have been calculated as mesh size changes. Since theoretical values of natural frequencies for a simple structure are known, the deviation between the numerical and theoretical values is obtained as a function of mesh size. The result shows that the error is no longer decreased if the mesh size becomes a quarter wavelength or smaller than that. Second, the mesh size effect is also investigated for the number of modes. For the frequency band up to 1.4 kHz, the structure should have 38 modes in total. As the mesh size reaches to the quarter wavelength, the total count in modes approaches to the same values. Third, a mobility function at the driving point is compared between SEA and FEM result. In SEA application, the mobility function is determined by the modal density and the mass of the structure. It is independent of excitation frequencies. When the mobility function is calculated from a wavelength to one-tenth of it, the mobility becomes constant if the mesh becomes a quarter wavelength or smaller. We can conclude that dynamic parameters, such as eigenvalues, mode count, and mobility function, can be correctly estimated, while saving the computing burden, if a quarter wavelength (.lambda./4) mesh is used. Therefore, (.lambda./4) mesh is recommended in structural vibration analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.5
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• pp.335-342
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• 2020

Tailless aircraft designed for stealth efficiency uses spoilers instead of rudders for the directional control. When the spoiler is rapidly deployed, highly nonlinear and unsteady aerodynamic characteristics can be generated, resulting in adverse effects on aircraft flight performance. This paper investigates the aerodynamic characteristics of an airfoil with moving spoiler using dynamic mesh CFD technique. The effects of spoiler operation speed, mounting location, and deployment scheduling are analyzed to reduce the adverse effects of the spoiler's dynamic operation. The results shows that the adverse effects of dynamic spoiler can be reduced by appropriate selection of the spoiler mounting location and deployment scheduling.

• Membrane and Water Treatment
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• v.9 no.4
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• pp.255-262
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• 2018

This study attempted to evaluate the process of self-forming dynamic membrane formation on mesh filter in membrane bioreactor with a two-stage method of batch (agitation) and continues (aeration) stage at different sludge concentrations. Four concentrations of activated sludge including $6{\pm}0.4$, $8{\pm}0.5$, $10{\pm}0.3$, $14{\pm}0.3g/L$ were used to demonstrate the optimal concentration of sludge for treating municipal wastewater and reducing fouling in dynamic membrane bioreactor. The formation time and effluent turbidity were decreased in the batch stage when increasing the activated sludge concentration. The minimum values of formation time and effluent turbidity were 14 min and 43 NTU for the optimum mixed liqueur suspended solids of $8{\pm}0.5g/L$, respectively. To improve operational condition and fouling reduction in the aeration stage, critical fluxes were measured for all concentrations by flux-step method. With increasing the sludge concentration, the relevant critical fluxes reduced. The optimum subcritical flux of $30L/m^2/h$ was applied as operating flux in the second stage. The maximum COD removal efficiency of 98% was achieved by the concentration of $8{\pm}0.5g/L$. Compressibility index of self-forming dynamic membrane and transmembrane pressure trend remained somewhat constant until the optimal concentration of $8{\pm}0.5g/L$ and thereafter they increased steeply.

• Korean Journal of Computational Design and Engineering
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• v.5 no.4
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• pp.347-358
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• 2000

The view dependency of typical spatial-partitioning based NC simulation methods is overcome by polygon rendering technique that generates polygons to represent the workpiece, thus enabling dynamic viewing transformations without reconstruction of the entire data structure. However, the polygon rendering technique still has difficulty in realizing real-time simulation due to unsatisfactory performance of current graphics devices. Therefore, it is necessary to develop a mesh decimation method that enables rapid rendering without loss of display quality. In this paper. we proposed a new mesh decimation algorithm thor a workpiece whose shape varies dynamically. In this algorithm, the 2-map data thor a given workpiece is divided into several regions, and a triangular mesh is constructed for each region first. Then, if any region it cut by the tool, its mesh is regenerated and decimated again. Since the range of mesh decimation is confined to a few regions, the reduced polygons for rendering can be obtained rapidly. Our method enables the polygon-rendering based NC simulation to be applied to the computers equipped with a wider range of graphics cards.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.12
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• pp.2744-2754
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• 1997

Recently, the Multi-Layer Restoration(MLR) algorithm was proposed by British Telecom(BT) to restore the network failures in Digital Cross-connect System(DCS) mesh survival network[1, 2]. This algorithm has multi restoration stage which is composed of the pre-planned and dynamic restoration. This algorithm is effective its ability in link or node failures. This reason is that it does not restore in the pre-planned rstoration stage but in dynamic restoration stage. In this paper, we propose the MLR with pre-planned Multi-Chooser(PMC) and successive restoration ratio algorithm. This proposed algorithm has a excellent performance for restortion time and ratio, spare channel availability and fast restoration from multiple link failure or node failure. This paper proposed the modeling and restoration algorithm, and analyzed the performance of the algorithm by simulation using OPNET(OPtimized Network Engineering Tools).

• The KSFM Journal of Fluid Machinery
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• v.12 no.3
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• pp.75-78
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• 2009

• Computational Structural Engineering
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• v.22 no.4
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• pp.13-18
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• 2009

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.6
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• pp.1077-1082
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• 2009

Wireless Mesh Network(WMN) is wireless backbone networks technique which has ease of network configuration and cost of advantage. Recently, WNM released a new product, but most of existing research and technology analysis the performance through the simulation. This paper build the wireless mesh network testbed for actual situation. Testbed supports multi-channel multi-interface using bridge, the Wireless Distribution System and dynamic location-based routing protocol. This routing protocol strongly design against wireless interference using metric for link channel change and real distance. Then, the address of mesh clients assigned by the centralized address management server. Mesh clients is designed and implemented to manage network through Simple Network Management Protocol.

• Wind and Structures
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• v.1 no.1
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• pp.111-125
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• 1998

This paper deals with the development of variable-node element and its application to the adaptive h-version mesh refinement-recovery for the incompressible viscous flow analysis. The element which has variable mid-side nodes can be used in generating the transition zone between the refined and unrefined element and efficiently used for the construction of a refined mesh without generating distorted elements. A modified Guassian quadrature is needed to evaluate the element matrices due to the discontinuity of derivatives of the shape functions used for the element. The penalty function method which can reduce the number of the independent variables is adopted for the purpose of computational efficiency and the selective reduced integration is carried out for the convection and pressure terms to preserve the stability of solution. For the economical analysis of transient problems in which the locations to be refined are changed in accordance with the dynamic distribution of velocity gradient, not only the mesh refinement but also the mesh recovery is needed. The numerical examples show that the optimal mesh for the finite element analysis of a wind around the structures can be obtained automatically by the proposed scheme.