New experimental results obtained from a high density polyethylene (HDPE) pipeline for transient conditions are presented and discussed. Transient pressure data at different pipe sections were collected. Peculiar feat...
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New experimental results obtained from a high density polyethylene (HDPE) pipeline for transient conditions are presented and discussed. Transient pressure data at different pipe sections were collected. Peculiar features were observed, which are typical of viscoelastic pipes, in particular, a significant damping of extreme pressures was observed in comparison to what is typically obtained for metal pipes. Physical constraints of the pipe are important to describe some vibrations observed in the system. The viscoelastic transient solver developed by Covas et al. (2005) was used to carry out numerical simulations of experimental tests. The comparison of numerical results with experimental data has shown that the viscoelastic model accurately predicts observed transient pressures. Additional considerations are carried out about the calibrated creep function for this test case in comparison with the ones obtained in previous researches.
The possibility of employing internal wall as mass absorber in rectangular water storage tanks subjected to harmonic ground motion excitation is investigated in this paper. Internal walls are usually used to lengthen ...
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The possibility of employing internal wall as mass absorber in rectangular water storage tanks subjected to harmonic ground motion excitation is investigated in this paper. Internal walls are usually used to lengthen the water path in the tank that could also be used as mass absorber to control seismic demand on tank's exterior walls. Derivation of the response of the coupled system including rigid external walls, flexible internal wall and fluid field is in frequency domain. The responses of the tank are evaluated subjected to harmonic excitations. By tuning the dynamic behavior of the tank and the sloshing liquid by changing the mass and stiffness of internal flexible wall, it is shown that wave elevation and water pressure on external rigid walls can be significantly reduced.
We have developed a numerical method for simulating viscous flow through a compliant closed tube,driven by a pair of fluid source and *** is natural for tubular flow simulations,the problem is formulated in axisymmetr...
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We have developed a numerical method for simulating viscous flow through a compliant closed tube,driven by a pair of fluid source and *** is natural for tubular flow simulations,the problem is formulated in axisymmetric cylindrical coordinates,with fluid flow described by the Navier-Stokes *** the tubular walls are assumed to be elastic,when stretched or compressed they exert forces on the *** these forces are singularly supported along the boundaries,the fluid velocity and pressure fields become *** accurately compute the solution,we use the velocity decomposition approach,according to which pressure and velocity are decomposed into a singular part and a remainder *** singular part satisfies the Stokes equations with singular boundary *** the Stokes solution is unsmooth,it is computed to second-order accuracy using the immersed interface method,which incorporates known jump discontinuities in the solution and derivatives into the finite difference *** remainder part,which satisfies the Navier-Stokes equations with a continuous body force,is *** equations describing the remainder part are discretized in time using the semi-Lagrangian approach,and then solved using a pressure-free projection *** results indicate that the computed overall solution is secondorder accurate in space,and the velocity is second-order accurate in time.
Rotational components of ground motion including rocking and torsional components have rarely been accounted for in designing and analyzing water storage tanks. In this paper, the effects of these components on the dy...
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Rotational components of ground motion including rocking and torsional components have rarely been accounted for in designing and analyzing water storage tanks. In this paper, the effects of these components on the dynamic response of water storage tanks are studied. The rotational components of ground motion acceleration have been obtained using an improved approach from the corresponding available translational components based on the transversely isotropic elastic wave propagation and classical elasticity theories. Based on this approach, it becomes possible to consider the frequency-dependent wave velocities and incident wave angle to generate the rotational components. For this purpose, the translational components of four earthquakes have been selected to generate their relative rotational components based on SV and SH wave incidence. The translational and computed rotational motions were then applied to the concrete elevated water storage tank with different water elevations considering fluid-structure interaction using the finite element method. The linear responses of these structures considering the full six components of the ground motion show that the rotational components of ground motion can affect the displacement and reaction force of the structure, depending on the frequency of structure and predominant frequencies of translational and rotational components of ground motion.
A partitioned numerical model for fluid-structure interaction analysis of incompressible flows and structures with geometrically non-linear behavior is presented in this work. The flow analysis is performed considerin...
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A partitioned numerical model for fluid-structure interaction analysis of incompressible flows and structures with geometrically non-linear behavior is presented in this work. The flow analysis is performed considering the well-known Navier-Stokes equations for Newtonian fluids and the continuity equation, obtained from the pseudo-compressibility hypothesis. An explicit two-step Taylor-Galerkin scheme is employed in the time discretization procedure of the system of governing equations, which is expressed in terms of an arbitrary Lagrangean-Eulerian description. The structural subsystem is analyzed using a geometrically non-linear elastic model and the respective equation of motion is discretized in the time domain employing the Generalized-a scheme. fluid-structure coupling is taken into account regarding a new energy-conserving partitioned scheme with non-linear effects, which is accomplished by enforcing equilibrium and kinematical compatibility conditions at the solid-fluid interface. Non-matching meshes and subcycling are also considered in the present model. The finite element method is employed for spatial discretizations using eight-node hexahedral elements with one-point integration in both fields. Some numerical examples are simulated in order to demonstrate the applicability of the proposed formulation. Copyright (C) 2009 John Wiley & Sons, Ltd.
This work simulates a complex fluid flow in fluid-structure interaction (FSI). The flow under consideration is governed by Navier-Stokes equations for incompressible viscous fluids and modeled with the finite volume m...
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This work simulates a complex fluid flow in fluid-structure interaction (FSI). The flow under consideration is governed by Navier-Stokes equations for incompressible viscous fluids and modeled with the finite volume method. Large eddy simulation is used to simulate the unsteady turbulent flow. The structure is representedby a finite element formulation. The present work introduces a strongly coupled partitioned approach that is applied to complex flow in fluid machinery. In this approach, the fluid and structure equations are solved separately using different solvers, but are implicitly coupled into one single module based on sensitivity analysis of the important displacement and stress modes. The applied modes and their responses are used to build up a reduced-order model. The proposed model is used to predict the unsteady flow fields of a 3D complete passage, involving in stay, guide vanes, and runner blades, for a Francis hydro turbine and FSI is considererd. The computational results show that a fairly good convergence solution is achieved by using the reduced-order model that is based on only a few displacement and stress modes, which largely reduces the computational cost, compared with traditional approaches. At the same time, a comparison of the numerical results of the model with available experimental data validates the methodology and assesses its accuracy. Copyright (C) 2008 John Wiley & Sons, Ltd.
Most aquatic animals propel themselves by flapping flexible appendages. To gain insight into the effect of flexibility on the swimming performance, we have studied experimentally an idealized system. It consists of a ...
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Most aquatic animals propel themselves by flapping flexible appendages. To gain insight into the effect of flexibility on the swimming performance, we have studied experimentally an idealized system. It consists of a flexible plate whose leading edge is forced into a harmonic heave motion, and which is immersed in a uniform flow. As the forcing frequency is gradually increased, resonance peaks are evidenced on the plate's response. In addition to the forcing frequency, the Reynolds number, the plate rigidity and the forcing amplitude have also been varied. In the range of parameters studied, the main effect on the resonance is due to the forcing amplitude, which reveals that non-linearities are essential in this problem. (c) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
This study investigated the effect of the initial transient hydrodynamic loading on dynamic responses of composite structures which move under water from the rest condition to a steady-state velocity for a given time ...
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This study investigated the effect of the initial transient hydrodynamic loading on dynamic responses of composite structures which move under water from the rest condition to a steady-state velocity for a given time duration with different acceleration profiles. Numerical analyses were conducted including the fluid-structure interaction. The computational model was validated against an experimental data, and various cases were examined numerically. The cases include various transient velocities of the structure, fluid boundary conditions, structural geometric configurations and material properties. The results showed that the peak fluid pressure and the resultant stresses in the composite structures are dependent on most of those parameters significantly. The maximum stresses under transient hydrodynamic loading could be an order of magnitude larger than those stresses under the final steady-state loading. A lighter composite structure experienced greater stresses and strains while the fluid pressure did not have any noticeable change under the same flow condition.
The prediction of flow rates at which the vibration-induced instability takes place in tubular heat exchangers due to cross flow is of major importance to the performance and service life of such equipment. In this pa...
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The prediction of flow rates at which the vibration-induced instability takes place in tubular heat exchangers due to cross flow is of major importance to the performance and service life of such equipment. In this paper, the semi-analytical model is developed and utilized to study the triangular tube patterns. The developed mathematical model is tuned with the experimentally measured fluid-elastic force coefficients. An experimental setup with water channel and instrumented test section is constructed. In this investigation, two test sections are constructed for both the normal triangular and the rotated triangular tube arrays. The developed scheme is utilized for predicting the critical flow velocities at the inception of flow-induced instability in the two triangular tube arrays. The results are compared to those obtained for two other bundle configurations, namely the square and rotated square arrays. The results of the two tube patterns are viewed in light of TEMA predictions. The comparisons demonstrated that TEMA predictions provided more conservative guidelines for all the configurations considered. Field application of the obtained results was successful in extending the service life of tube and shell heat exchangers beyond that predicted by TEMA.
Over the last decade the Lattice Boltzmann method, which was derived from the kinetic gas theory, has matured as an efficient approach for solving Navier-Stokes equations. The p-FEM approach has proved to be highly ef...
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Over the last decade the Lattice Boltzmann method, which was derived from the kinetic gas theory, has matured as an efficient approach for solving Navier-Stokes equations. The p-FEM approach has proved to be highly efficient for a variety of problems in the field of structural mechanics. Our goal is to investigate the validity and efficiency of coupling the two approaches to simulate transient bidirectional fluid-structure interaction problems with geometrically non-linear structural deflections. A benchmark configuration of self-induced large oscillations for a flag attached to a cylinder can be accurately and efficiently reproduced within this setting. We describe in detail the force evaluation techniques, displacement transfers and the algorithm used to couple these completely different solvers as well as the results, and compare them with a benchmark reference solution computed by a monolithic finite element approach. Copyright (0 2009 John Wiley & Sons, Ltd.
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