• Title/Summary/Keyword: Layered flow

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Radial flow advancement in multi-layered preform for resin transfer molding

  • Shin, K.S.;Song, Y.S.;Youn, J.R.
    • Korea-Australia Rheology Journal
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    • v.18 no.4
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    • pp.217-224
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    • 2006
  • Rapid flow advancement without void formation is essential in the liquid composite molding (LCM) such as resin transfer molding (RTM) and vacuum assisted resin transfer molding (VARTM). A highly permeable layer in multi-layered preform has an important role in improvement of the flow advancement. In this study, a multi-layered preform which consists of three layers is employed. Radial flow experiment is carried out for the multi-layered preform. A new analytic model for advancement of flow front is proposed and effective permeability is defined. The effective permeability for the multi-layered preform is obtained analytically and compared with experimental results. Compaction test is performed to determine the exact fiber volume traction of each layer in the multi-layered preform. Transverse permeability employed in modeling is measured experimentally unlike the previous studies. Accurate prediction of flow advancement is of great use for saving the processing time and enhancing product properties of the final part.

A Study on Resin Flow through a Multi-layered Preform in Resin Transfer Molding (수지이송성형시 다층 예비성형체 내부에서의 수지유동 및 투과 계수에 관한 연구)

  • Seong, Dong-Gi;Youn, Jae-Ryoun
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2001.05a
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    • pp.176-179
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    • 2001
  • When the preform is composed of more than two layers with different in-plane permeability in resin transfer molding, effective average permeability should be determined for the flow analysis in the mold. The most frequently used averaging scheme is the weighted average scheme, but it does not account for the transverse flow between adjacent layers. A new averaging scheme is proposed predicting the effective permeability of the multi-layered preform, which accounts for the transverse flow effect. The new scheme is verified by measuring the effective permeability of the multi-layered preforms and the difference in each flow front position.

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Three-Dimensional Mold Filling Simulation for Multi-layered Preform in Resin Transfer Molding (다층 예비성형체에 대한 삼차원 충진해석)

  • Yang, Mei;Song, Young-Seok;Youn, Jae-Roun
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2005.04a
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    • pp.137-140
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    • 2005
  • Resin transfer molding (RTM) is one of the most popular processes for producing fiber reinforced polymer composites. In the manufacture of complex thick composite structures, analysis on flow front advancement on the resin impregnating the multi-layered fiber preform is helpful for the optimization of the process. In this study, three-dimensional mold filling simulation of RTM is carried out by using CVFEM (Control Volume Finite Element Method). On the assumption of isothermal flow of Newtonian fluid, Darcy’s law and continuity equation are used as governing equations. Different permeability tensors employed in each layer are obtained by experiments. Numerically predicted flow front is compared with experimental one in order to validate the numerical results. Flow simulations are conducted in the two mold geometries, rectangular plate and hollow cylinder. Permeability tensor of each layer preform in Cartesian coordinate system is transformed to cylinder coordinates system so that the flow within the multi-layered preforms of the hollow cylinder can be calculated exactly. Our emphasis is on the three dimensional flow analysis for circular three-dimensional braided preform, which shows outstanding mechanical properties such as high impact strength and toughness compared with other conventional two-dimensional laminar-structured preforms.

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Experimental and Theoretical Study on Shear Flow Behavior of Polypropylene/Layered Silicate Nanocomposites

  • Lee, Seung-Hwan;Youn, Jae-Ryoun
    • Advanced Composite Materials
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    • v.17 no.3
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    • pp.191-214
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    • 2008
  • Polypropylene/layered silicate nanocomposites containing maleic anhydride grafted polypropylene were prepared by melt compounding and their rheological behavior was investigated in shear flow. Transient and steady shear flows were simulated numerically by using the K-BKZ integral constitutive equation along with experimentally determined damping functions under dynamic oscillatory and step strain shear flows. Nonlinear shear responses were predicted with the K-BKZ constitutive equation using two different damping functions such as the Wagner and PSM models. It was observed that PP-g-MAH compatibilized PP/layered silicate nanocomposites have stronger and earlier shear thinning and higher steady shear viscosity than pure PP resin or uncompatibilized nanocomposites at low shear rate regions. Strong damping behavior of the PP/layered silicate nanocomposite was predicted under large step shear strain and considered as a result of the strain-induced orientation of the organoclay in the shear flow. Steady shear viscosity of the pure PP and uncompatibilized nanocomposite predicted by the K-BKZ model was in good agreement with the experimental results at all shear rate regions. However, the model was inadequate to predict the steady shear viscosity of PP-g-MAH compatibilized nanocomposites quantitatively because the K-BKZ model overestimates strain-softening damping behavior for PP/layered silicate nanocomposites.

Numerical Study on Double-Diffusive Convection in a Stratified Trapezoidal Enclosure (성층화된 사다리꼴 용기내에서의 이중확산유동에 관한 수치해석)

  • 현명택
    • Journal of Ocean Engineering and Technology
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    • v.6 no.2
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    • pp.143-150
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    • 1992
  • Numerical simulation is made of a stably stratified salt-water solution due to lateral heating in an equilateral trapezoidal enclosure using boundary-fitted coordinate in grid generation. Results show four types of the global fluid pattern depending on the buoyancy ratio in the enclosure, i.e., unicell flow pattern for the low buoyancy ratio, layered flow pattern for the increasing buoyancy ratio, layered flow pattern with stagnant zone for the relatively high buoyancy ratio and stagnant flow pattern for the much higher buoyancy ratio.

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Rheological Behavior of Polymer/Layered Silicate Nanocomposites under Uniaxial Extensional Flow

  • Park Jun-Uk;Kim Jeong-Lim;Kim Do-Hoon;Ahn Kyung-Hyun;Lee Seung-Jong;Cho Kwang-Soo
    • Macromolecular Research
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    • v.14 no.3
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    • pp.318-323
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    • 2006
  • We investigated the rheological behaviors and orientation of three different types of layered silicate composite systems under external flow: microcomposite, intercalated and exfoliated nanocomposites. Rheological measurements under shear and uniaxial extensional flows, two-dimensional, small-angle X-ray scattering and transmission electron microscopy were conducted to investigate the properties, as well as nano- and micro-structural changes, of polymer/layered silicate nanocomposites. The preferred orientation of the silicate layers to the flow direction was observed under uniaxial extensional flow for both intercalated and exfoliated systems, while the strain hardening behavior was observed only in the exfoliated systems. The degree of compatibility between the polymer matrix and clay determined the microstructure of polymer/clay composites, strain hardening behavior and spatial orientation of the clays under extensional flow.

Development a numerical model of flow and contaminant transport in layered soils

  • Ahmadi, Hossein;Namin, Masoud M.;Kilanehei, Fouad
    • Advances in environmental research
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    • v.5 no.4
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    • pp.263-282
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    • 2016
  • Contaminant transport in groundwater induces major threat and harmful effect on the environment; hence, the fate of the contaminant migration in groundwater is seeking a lot of attention. In this paper a two dimensional numerical flow and transport model through saturated layered soil is developed. Groundwater flow and solute transport has been simulated numerically using proposed model. The model implements the finite volume time splitting method to discretize the main equations. The performance, accuracy and efficiency of the out coming numerical models have been successfully examined by two test cases. The verification test cases consist of two-dimensional, groundwater flow and solute transport. The final purpose of this paper is to discuss and compare the shape of contaminant plume in homogeneous and heterogeneous media with different soil properties and control of solute transport using a zone for minimizing the potential of groundwater contamination; furthermore, this model leads to select the effective and optimum remedial strategies for cleaning the contaminated aquifers.

A Layered Network Flow Algorithm for the Tunnel Design Problem in Virtual Private Networks with QoS Guarantee

  • Song, Sang-Hwa;Sung, Chang-Sup
    • Management Science and Financial Engineering
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    • v.12 no.2
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    • pp.37-62
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    • 2006
  • This paper considers the problem of designing logical tunnels in virtual private networks considering QoS guarantee which restricts the number of tunnel hops for each traffic routing. The previous researches focused on the design of logical tunnel itself and Steiner-tree based solution algorithms were proposed. However, we show that for some objective settings it is not sufficient and is necessary to consider both physical and logical connectivity at the same time. Thereupon, the concept of the layered network is applied to the logical tunnel design problem in virtual private networks. The layered network approach considers the design of logical tunnel as well as its physical routing and we propose a modified branch-and-price algorithm which is known to solve layered network design problems effectively. To show the performance of the proposed algorithm, computational experiments have been done and the results show that the proposed algorithm solves the given problem efficiently and effectively.

Collapse analysis of shallow tunnel subjected to seepage in layered soils considering joined effects of settlement and dilation

  • Yang, X.L.;Zhang, R.
    • Geomechanics and Engineering
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    • v.13 no.2
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    • pp.217-235
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    • 2017
  • The stability prediction of shallow buried tunnels is one of the most difficult tasks in civil engineering. The aim of this work is to predict the state of collapse in shallow tunnel in layered soils by employing non-associated flow rule and nonlinear failure criterion within the framework of upper bound theorem. Particular emphasis is first given to consider the effects of dilation on the collapse mechanism of shallow tunnel. Furthermore, the seepage forces and surface settlement are considered to analyze the influence of different dilation coefficients on the collapse shape. Two different curve functions which describe two different soil layers are obtained by virtual work equations under the variational principle. The distinct characteristics of falling blocks up and down the water level are discussed in the present work. According to the numerical results, the potential collapse range decreases with the increase of the dilation coefficient. In layered soils, both of the single layer's dilation coefficient and two layers' dilation coefficients increase, the range of the potential collapse block reduces.

Collapse mechanism of tunnel roof considering joined influences of nonlinearity and non-associated flow rule

  • Yang, X.L.;Xu, J.S.;Li, Y.X.;Yan, R.M.
    • Geomechanics and Engineering
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    • v.10 no.1
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    • pp.21-35
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    • 2016
  • Employing non-associated flow rule and Power-Law failure criterion, the failure mechanisms of tunnel roof in homogeneous and layered soils are studied in present analysis. From the viewpoint of energy, limit analysis upper bound theorem and variation principle are introduced to study the influence of dilatancy on the collapse mechanism of rectangular tunnel considering effects of supporting force and seepage force. Through calculation, the collapsing curve expressions of rectangular tunnel which are excavated in homogeneous soil and layered soils respectively are derived. The accuracy of this work is verified by comparing with the existing research results. The collapsing surface shapes with different dilatancy coefficients are draw out and the influence of dilatancy coefficient on possible collapsing range is analyzed. The results show that, in homogeneous soil, the potential collapsing range decreases with the decrease of the dilatancy coefficient. In layered soils, the total height and the width on the layered position of possible collapsing block increase and the width of the falling block on tunnel roof decrease when only the upper soil's dilatancy coefficient decrease. When only the lower soil's dilatancy coefficient decrease or both layers' dilatancy coefficients decrease, the range of the potential collapsing block reduces.