• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.645-653
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• 1996

In order to avoid pathological mesh dependency in finite element modelling of strain localization, an isotropic elasto-plastic model with a yield function depending on the Laplacian of the equivalent plastic strain is implemented in a 4-node quadrilateral finite element with one integration point based on a mixed formulation derived from Hu-Washizu principle. The evaluation of the Laplacian is based on a least square polynomial approximation of the equivalent plastic strain around each integration point. This non local approach allows to satisfy exactly the consistency condition at each integration point. Some examples are treated to illustrate the effectiveness of the method.

• Geomechanics and Engineering
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• v.7 no.4
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• pp.335-353
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• 2014

The softening hyperelastic model based on the strain energy limitation is of clear concepts and simple forms to describe the failure of materials. In this study, a linear and a nonlinear softening hyperelastic model are proposed to characterize the deformation and the failure in granular materials by introducing a softening function into the shear part of the strain energy. A method to determine material parameters introduced in the models is suggested. Based on the proposed models the numerical examples focus on bearing capacity and strain localization of granular materials. Compared with Volokh softening hyperelasticity and classical Mohr-Coulomb plasticity, our proposed models are able to capture the typical characters of granular materials such as the strain softening and the critical state. In addition, the issue of mesh dependency of the proposed models is investigated.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.5
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• pp.61-68
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• 2021

Movable weirs with multi-stage control are necessary in many Korean rivers to actively control the water storage level. A mesh dependency test was performed to determine the appropriate number of meshes for structural analysis of movable weirs. The standing angles of movable weirs were set to 60°, 45°, 30°, and 15° for stress analysis. The standing angle of 0° was excluded from the analysis because it was unloaded. Changes in the standing angle led to changes in the water depth, maximum pressure, maximum strain, and maximum stress. The maximum average stress and the structural safety of the multi-stage control movable weir were computed and tested using the Ansys FEA software package.

• Structural Engineering and Mechanics
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• v.77 no.4
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• pp.523-533
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• 2021

The present study investigates the lateral torsional buckling behaviour of pultruded glass fiber reinforced polymer (GFRP) simply supported channel beams subjected to uniform bending about their major axis. A parametric study by varying the sectional geometry and span of channel beams is carried out by using ABAQUS software. The accuracy of the FE models was ensured by verifying them against the available results provided in the literature. The effect of geometric nonlinearity, geometric imperfections, and the dependency of finite element mesh on the lateral torsional buckling were carefully considered in the FE model. Lateral torsional buckling (LTB) strengths obtained from the numerical study were compared with the theoretical LTB strengths obtained based on the Eurocode 3 approach for steel sections. The comparison between the numerical strengths and the design procedure proposed in the literature based on Eurocode 3 approach revealed disagreements. Therefore, a simplified improved design procedure is proposed for the safe design strength prediction of pultruded GFRP channel beams. The proposed equation has been provided that might aid the structural engineers in economically designing the pultruded GFRP channel beams in the future.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.4
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• pp.87-93
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• 2009

Wireless mesh networks (WMNs) are emerging technologies that provide ubiquitous environments and wireless broadband access. The aggregate capacity of WMNs can be improved by minimizing the effect of channel interference. The IEEE 802.11b/g standard which is mainly used for the network interface technology in WMNs provides 3 multiple channels. We must consider the channel scanning delay and the channel dependency problem to effectively assign channels in like these multi-channel WMNs. This paper proposes a cluster-based channel assignment (CB-CA) algorithm for multi-channel WMNs to solve such problems. The CB-CA does not perform the channel scanning and the channel switching through assigning co-channel to the inter-cluster head (CH) links. In the CB-CA, the communication between the CH and cluster member (CM) nodes uses a channel has no effect on channels being used by the inter-CH links. Therefore, the CB-CA can minimize the interference within multi-channel environments. Our simulation results show that CB-CA can improve the performance of WMNs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12B
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• pp.1050-1057
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• 2008

Wireless Mesh Networks (WMNs) have recently become a hot issue to support high link capacity in wireless access networks. The IEEE 802. I 1 standard which is mainly used for the network interface technology in WMNs supports up to 3 or 12 multiple channels according to the IEEE 802.11 specification. However, two important problems must be addressed when we design a channel assigmnent algorithm: channel dependency problem and channel scanning delay. The former occurs when the dynamic channel switching of an interface leads to the channel switching of other interfaces to maintain node connectivity. The latter happens per channel switching of the interface, and affects the network performance. Therefore, in this paper, we propose the Distance-Based Channel Assigmnent (DB-CA) scheme for multi-channel WMNs to solve such problems. In DB-CA, nodes just perform channel switching without channel scanning to communicate with neighboring nodes that operate on different channels. Furthermore, DB-CA minimizes the interference of channels being used by nodes near the gateway in WMNs. Our simulation results show that DB-CA achieves improved performance in WMNs.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.41-52
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• 2021

During atmospheric ascent of a launch vehicle, airborne acoustic loads act on the vehicle and its effect becomes pronounced at transonic speed. In the present study, acoustic loads acting on a hammerhead launch vehicle at a transonic speed have been analyzed using ��-ω SST based IDDES and the results including mean Cp, Cprms, and PSD are compared to available wind-tunnel test data. Mesh dependency of IDDES results has been investigated and it has been concluded that with an appropriate turbulence scale-resolving computational mesh, the characteristic flow features around a transonic hammerhead launch vehicle such as separated shear flow at fairing shoulder and its reattachment on rear body as well as large pressure fluctuation in the region of separated flow behind the boat-tail can be predicted with reasonable accuracy for engineering purposes.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.5
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• pp.407-417
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• 2015

For the more accurate prediction on manoeuvring performance of a ship at initial design phase, bare hull manoeuvring coefficients were estimated by RANS(Reynolds Averaged Navier-Stokes) based virtual captive model tests. Hydrodynamic forces and moment acting on the hull during static drift and harmonic oscillatory motions were computed with a commercial RANS code STAR-CCM+. Automatic and consistent mesh generation could be implemented by using macro functions of the code and user dependency could be greatly reduced. Computed forces and moments on KCS and KVLCC 1&2 were compared with the corresponding measurements from PMM(Planar Motion Mechanism) tests. Quite good agreement can be observed between the CFD and EFD results. Manoeuvring coefficients and IMO standard manoeuvres estimated from the computed data also showed reasonable agreement with those from the experimental data. Based on these results, we could confirm that the developed virtual captive manoeuvring model test process could be applied to evaluate manoeuvrability of a ship at the initial hull design phase.

• Journal of computational fluids engineering
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• v.19 no.1
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• pp.64-72
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• 2014

This study aimed at assessing the analysis capability of thermal-hydraulic computer code, MARS for the behaviors of the core make-up tank (CMT). The sensitivity study on the nodalization to simulate the CMT was conducted, and the MARS calculations were compared with KAIST experimental data and RELAP5/MOD3.3 calculations. The 12-node model was fixed through a nodalization study to investigate the effect of the number of nodes in the CMT (2-, 4-, 8-, 12-, 16-node). The sensitivity studies on various parameters, such as water subcooling of the CMT, steam pressure, and natural circulation flow were done. MARS calculations were reasonable in the injection time and the effects of several parameters on the CMT behaviors even though the mesh-dependency should be properly treated for reactor applications.

• Structural Engineering and Mechanics
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• v.37 no.2
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• pp.197-213
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• 2011

Concrete is a heterogeneous material exhibiting quasi-brittle behaviour. While homogenization of concrete is commonly accepted in general engineering applications, a detailed description of the material heterogeneity using a mesoscale model becomes desirable and even necessary for problems where drastic spatial and time variation of the stress and strain is involved, for example in the analysis of local damages under impact, shock or blast load. A mesoscale model can also assist in an investigation into the underlying mechanisms affecting the bulk material behaviour under various stress conditions. Extending from existing mesoscale model studies, where use is often made of specialized codes with limited capability in the material description and numerical solutions, this paper presents a mesoscale computational model developed under a general-purpose finite element environment. The aim is to facilitate the utilization of sophisticated material descriptions (e.g., pressure and rate dependency) and advanced numerical solvers to suit a broad range of applications, including high impulsive dynamic analysis. The whole procedure encompasses a module for the generation of concrete mesoscale structure; a process for the generation of the FE mesh, considering two alternative schemes for the interface transition zone (ITZ); and the nonlinear analysis of the mesoscale FE model with an explicit time integration approach. The development of the model and various associated computational considerations are discussed in this paper (Part 1). Further numerical studies using the mesoscale model for both quasi-static and dynamic loadings will be presented in the companion paper (Part 2).