Interfacial stresses in damaged RC beams strengthened by externally bonded prestressed GFRP laminate plate: Analytical and numerical study

Chergui, Selma,Daouadji, Tahar Hassaine,Hamrat, Mostefa,Boulekbache, Bensaid,Bougara, Abdelkader,Abbes, Boussad,Amziane, Sofiane Techno-Press 2019 Advances in materials research Vol.8 No.3

In this study, the interfacial stresses in RC beams strengthened by externally bonded prestressed GFRP laminate are evaluated using an analytical approach, based on the equilibrium equations and boundary conditions. A comparison of the interfacial stresses obtained from the present analytical model and other existing models is undertaken. Otherwise, a parametric study is conducted to investigate the effects of geometrical and material properties on the variation of interfacial stresses in damaged RC beams strengthened by externally bonded prestressed GFRP laminate. The results obtained indicate that the damage degree has little effect on the maximum shear stress, with a variation less than 5% between the damaged and undamaged RC beams. However, the results also reveal that the prestressing level has a significant effect on the interfacial stresses; hence the damaged RC beam strengthened with an initial prestressing force of 100 kN gives 110% higher maximum shear stress than the damaged RC beam strengthened with an initial prestressing force of 50 kN. The values of shear stress obtained by the analytical approach are approximately equal to 44% of those obtained from the numerical solution, while the interfacial normal stresses predicted by the numerical study are approximately 26% higher than those calculated by the analytical solution.

A hybrid interface tracking – level set technique for multiphase flow with soluble surfactant

Shin, Seungwon,Chergui, Jalel,Juric, Damir,Kahouadji, Lyes,Matar, Omar K.,Craster, Richard V. Elsevier 2018 Journal of computational physics Vol.359 No.-

<P><B>Abstract</B></P> <P>A formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu and Tryggvason (JCP 274 (2014) 737–757) is adapted to the context of the Level Contour Reconstruction Method, LCRM, (Shin et al. IJNMF 60 (2009) 753–778, ) which is a hybrid method that combines the advantages of the Front-tracking and Level Set methods. Particularly close attention is paid to the formulation and numerical implementation of the surface gradients of surfactant concentration and surface tension. Various benchmark tests are performed to demonstrate the accuracy of different elements of the algorithm. To verify surfactant mass conservation, values for surfactant diffusion along the interface are compared with the exact solution for the problem of uniform expansion of a sphere. The numerical implementation of the discontinuous boundary condition for the source term in the bulk concentration is compared with the approximate solution. Surface tension forces are tested for Marangoni drop translation. Our numerical results for drop deformation in simple shear are compared with experiments and results from previous simulations. All benchmarking tests compare well with existing data thus providing confidence that the adapted LCRM formulation for surfactant advection and diffusion is accurate and effective in three-dimensional multiphase flows with a structured mesh. We also demonstrate that this approach applies easily to massively parallel simulations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Extension of the LCRM Front-tracking method (Shin et al. IJNMF 60 (2009) 753–778) to flows with surfactant. </LI> <LI> Following Muradoglu and Tryggvason (JCP 274 (2014) 737–757) surfactant transport is solved on the interface and in the bulk. </LI> <LI> Accuracy demonstrated for mass conservation, surface advection and diffusion, bulk transport and Marangoni stresses. </LI> <LI> Large scale parallel calculations of two-phase annular film flow in the counter-current flow regime. </LI> </UL> </P>

A solver for massively parallel direct numerical simulation of three-dimensional multiphase flows

Shin, S.,Chergui, J.,Juric, D. Springer Science + Business Media 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.4

<P>We present a new solver for massively parallel simulations of fully three-dimensional multiphase flows. The solver runs on a variety of computer architectures from laptops to supercomputers and on 262144 threads or more (limited only by the availability to us of more threads). The code is wholly written by the authors in Fortran 2008 and uses a domain decomposition strategy for parallelization with MPI. The fluid interface solver is based on a parallel implementation of the LCRM hybrid front tracking/level set method designed to handle highly deforming interfaces with complex topology changes. We discuss the implementation of this interface method and its particular suitability to distributed processing where all operations are carried out locally on distributed subdomains. We have developed parallel GMRES and Multigrid iterative solvers suited to the linear systems arising from the implicit solution of the fluid velocities and pressure in the presence of strong density and viscosity discontinuities across fluid phases. Particular attention is drawn to the details and performance of the parallel Multigrid solver. The code includes modules for flow interaction with immersed solid objects, contact line dynamics, species and thermal transport with phase change. Here, however, we focus on the simulation of the canonical problem of drop splash onto a liquid film and report on the parallel performance of the code on varying numbers of threads. The 3D simulations were run on mesh resolutions up to 1024(3) with results at the higher resolutions showing the fine details and features of droplet ejection, crown formation and rim instability observed under similar experimental conditions.</P>

Direct simulation of multiphase flows with modeling of dynamic interface contact angle

Shin, Seungwon,Chergui, Jalel,Juric, Damir Springer-Verlag 2018 Theoretical and computational fluid dynamics Vol.32 No.5

Optical Properties of ZnO Aggregates in a KBr Matrix

M. SAMAH,A. CHERGUI,M. BOUGUERRA,M. Kerkar,M.A. BELKHIR,N. Maloufi 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.5I

Zinc oxide nanocrystals were prepared, using the Czochralsk¨ı method of growth, in a KBr matrix during pulling. Good evidence was found for the quantum confinement effect being special quality of this nanosystem. As an indication of the quantum confinement effect, excellent emissions from the band edge have been observed in the optical absorption and selective PLspectra. The XRD spectrum exhibits a preferential insertion of ZnO aggregates within the KBr matrix.

Hybridization of front tracking and level set for multiphase flow simulations: a machine learning approach

Ikroh Yoon,Jalel Chergui,Damir Juric,신승원 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.9

A machine learning (ML) based approach is proposed to hybridize two wellestablished methods for multiphase flow simulations: the front tracking (FT) and the level set (LS) methods. Based on the geometric information of the Lagrangian marker elements which represents the phase interface in FT simulations, the distance function field, which is the key feature for describing the interface in LS simulations, is predicted using an ML model. The trained ML model is implemented in our conventional numerical framework, and we finally demonstrate that the FT-based interface representation can easily and immediately be switched to an LS-based representation whenever needed during the simulation period.

Simulation of immiscible liquid–liquid flows in complex microchannel geometries using a front-tracking scheme

Kahouadji, Lyes,Nowak, Emilia,Kovalchuk, Nina,Chergui, Jalel,Juric, Damir,Shin, Seungwon,Simmons, Mark J. H.,Craster, Richard V.,Matar, Omar K. Springer Berlin Heidelberg 2018 MICROFLUIDICS AND NANOFLUIDICS Vol.22 No.11

<P>The three-dimensional two-phase flow dynamics inside a microfluidic device of complex geometry is simulated using a parallel, hybrid front-tracking/level-set solver. The numerical framework employed circumvents numerous meshing issues normally associated with constructing complex geometries within typical computational fluid dynamics packages. The device considered in the present work is constructed via a module that defines solid objects by means of a static distance function. The construction combines primitive objects, such as a cylinder, a plane, and a torus, for instance, using simple geometrical operations. The numerical solutions predicted encompass dripping and jetting, and transitions in flow patterns are observed featuring the formation of drops, ‘pancakes’, plugs, and jets, over a wide range of flow rate ratios. We demonstrate the fact that vortex formation accompanies the development of certain flow patterns, and elucidate its role in their underlying mechanisms. Experimental visualisation with a high-speed imaging are also carried out. The numerical predictions are in excellent agreement with the experimental data.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1007/s10404-018-2149-y) contains supplementary material, which is available to authorized users.</P>

Numerical simulation of supersquare patterns in Faraday waves

Kahouadji, L.,Pé,rinet, N.,Tuckerman, L. S.,Shin, S.,Chergui, J.,Juric, D. Cambridge University Press 2015 Journal of fluid mechanics Vol.772 No.-

<P>We report the first simulations of the Faraday instability using the full three-dimensional Navier–Stokes equations in domains much larger than the characteristic wavelength of the pattern. We use a massively parallel code based on a hybrid front-tracking/level-set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. Simulations performed in square and cylindrical domains yield complex patterns. In particular, a superlattice-like pattern similar to those of Douady &amp; Fauve (<I>Europhys. Lett.</I>, vol. 6, 1988, pp. 221–226) and Douady (<I>J. Fluid Mech.</I>, vol. 221, 1990, pp. 383–409) is observed. The pattern consists of the superposition of two square superlattices. We conjecture that such patterns are widespread if the square container is large compared with the critical wavelength. In the cylinder, pentagonal cells near the outer wall allow a square-wave pattern to be accommodated in the centre.</P>

Hysteretic Faraday waves

Pé,rinet, Nicolas,Falcó,n, Claudio,Chergui, Jalel,Juric, Damir,Shin, Seungwon American Physical Society 2016 Physical Review E Vol.93 No.6