Fluid Finite Element Research Articles

Stochastic seismic response of fluid and fluid–solid systems

The present paper presents a stochastic seismic analysis of fluid and fluid–solid systems by using Lagrangian approach. For this reason, authors have programmed variable-number-nodes two-dimensional isoparametric fluid finite elements in fortran and have incorporated into a generalpurpose computer program for stochastic dynamic analysis of structure systems, stocal. For numerical examples, a rigid fluid tank and a fluid–solid interaction system are selected. Natural frequencies from the modal analyses of the fluid and fluid–solid systems are compared with those of analytical and numerical solutions. S16E component of the Pacoima Dam record of the San Fernando Earthquake in 1971 is used as a ground motion. The mean of maximum values from stochastic analysis are compared with deterministic analysis results

Modal analysis of fluid-structure interaction problems with pressure-based fluid finite elements for industrial applications

The present paper deals with numerical developments performed in the finite element code ANSYS in order to carry out coupled fluid-structure analysis with pressure-based formulation. As a result, enhancement of the modeling possibilities within ANSYS is carried out for the following fluid and fluid structure modes: i) fluid sloshing modes, ii) fluid and fluid-structure modes with pressure-displacement formulation in axi-symmetric geometry with non axi-symmetric loading, iii) fluid-structure modes with symmetric formulations for elasto-acoustic and hydro-elastic problems, using the so-called symmetric (u, p, φ) and (u, η, φ) formulations. The paper also aims at providing finite element code users with test cases to refer to, for application of the new FSI formulations. The paper also serves as an introduction to the numerical calculation of eigenvalue problems with FSI. Theoretical bases of the formulations are first exposed; test-cases and industrial applications are then proposed. It is shown in particul...

Dynamic analysis of fluid–structure interaction problems with modal methods using pressure-based fluid finite elements

The present paper deals with numerical developments performed in the finite element code ANSYS in order to produce coupled fluid–structure dynamic analysis with pressure-based formulation, using modal and spectral methods. Enhancement of the modelling possibilities within the ANSYS code is carried out with implementation of fluid–structure symmetric formulations for elasto-acoustic and hydro-elastic problems, using the so-called symmetric ( u , p , ϕ ) and ( u , η , ϕ ) formulations. Using symmetric formulation enables linear dynamic analysis with modal projection techniques for a fluid–structure coupled system. The paper briefly recalls the basic principles of such methods in the context of FSI. Validation of the developments performed in the ANSYS code is exposed, focusing in particular on the calculation of effective mass for coupled eigenmodes. Industrial application is also presented and gives a validation test case for modal and spectral methods with FSI modelling.

Modelling of Effect of Inflow Turbulence on Large Eddy Simulation of Bluff Body Flows

A random flow generation (RFG) algorithm for a previously established large eddy simulation (LES) code is successfully incorporated into a finite element fluid flow solver to generate the required inflow/initial turbulence boundary conditions for the LES computations of viscous incompressible turbulent flow over a nominally twodimensional circular cylinder at Reynolds number of 140,000. The effect of generated turbulent inflow boundary conditions on the near wake flow and the shear layer and on the prediction of integral flow parameters is studied based on long time average results. No-slip velocity boundary function is used but wall effects are taken into consideration with a near wall modelling methodology based on van Driest Damping approach. The numerical results obtained from simulations are compared with each other and with the experimental data for different turbulent inflow boundary conditions to assess the functionality of the RFG algorithm for the present LES code and hence its influence on the vortex shedding mechanism and the resulting flow field predictions.

Modeling of Effect of Inflow Turbulence Data on Large Eddy Simulation of Circular Cylinder Flows

A random flow generation (RFG) algorithm for a previously established large eddy simulation (LES) code is successfully incorporated into a finite element fluid flow solver to generate the required inflow/initial turbulence boundary conditions for the three-dimensional (3D) LES computations of viscous incompressible turbulent flow over a nominally two-dimensional (2D) circular cylinder at Reynolds number of 140,000. The effect of generated turbulent inflow boundary conditions on the near wake flow and the shear layer and on the prediction of integral flow parameters is studied based on long time average results. Because the near-wall region cannot be resolved for high Reynolds number flows, no-slip velocity boundary function is used, but wall effects are taken into consideration with a near-wall modeling methodology that comprises the no-slip function with a modified form of van Driest damping approach to reduce the subgrid length scale in the vicinity of the cylinder wall. Simulations are performed for a 2D and a 3D configuration, and the simulation results are compared to each other and to the experimental data for different turbulent inflow boundary conditions with varying degree of inflow turbulence to assess the functionality of the RFG algorithm for the present LES code and, hence, its influence on the vortex shedding mechanism and the resulting flow field predictions.

Fluid-Structure Interaction Analysis of Flow-Induced Deformation in a Two-Phase, Neo-Hookean Marine Egg

Coupled computational fluid dynamics and finite element analyses were used to determine the material properties of the egg and jelly layer of the sea urchin Arbacia punctulata. Prior experimental shear flow results were used to provide material parameters for these simulations. A Neo-Hookean model was used to model the hyperelastic behaviors of the jelly layer and egg. A simple compressive simulation was then performed, to compare the maximum von Mises stresses within eggs, with and without jelly layers. Results of this study showed that (1) shear moduli range from ∼100to160Pa, and ∼40to140Pa for an egg without a jelly layer, and jelly layer itself, respectively; and (2) the presence of the jelly layer significantly reduces maximum von Mises stress in an egg undergoing compression.

A framework for design optimization using surrogates

Design optimization is a computationally expensive process as it requires the assessment of numerous designs and each of such assessments may be based on expensive analyses (e.g. computational fluid dynamics method or finite element based method). One way to contain the computational time within affordable limits is to use computationally cheaper approximations (surrogates) in lieu of the actual analyses during the course of optimization. This article introduces a framework for design optimization using surrogates. The framework is built upon a stochastic, zero-order, population-based optimization algorithm, which is embedded with a modified elitism scheme, to ensure convergence in the actual function space. The accuracy of the surrogate model is maintained via periodic retraining and the number of data points required to create the surrogate model is identified by a k-means clustering algorithm. A comparison is provided between different surrogate models (Kriging, radial basis functions (Exact and Fixed) and Cokriging) using a number of mathematical test functions and engineering design optimization problems. The results clearly indicate that for a given fixed number of actual function evaluations, the surrogate assisted optimization model consistently performs better than a pure optimization model using actual function evaluations.

Stochastic analysis of fluid-structure interaction systems by Lagrangian approach

In the present paper it is aimed to perform the stochastic dynamic analysis of fluid and fluidstructure systems by using the Lagrangian approach. For that reason, variable-number-nodes twodimensional isoparametric fluid finite elements are programmed in Fortran language by the authors and incorporated into a general-purpose computer program for stochastic dynamic analysis of structure systems, STOCAL. Formulation of the fluid elements includes the effects of compressible wave propagation and surface sloshing motion. For numerical example a rigid fluid tank and a dam-reservoir interaction system are selected and modeled by finite element method. Results obtained from the modal analysis are compared with the results of the analytical and numerical solutions. The Pacoima Dam record S16E component recorded during the San Fernando Earthquake in 1971 is used as a ground motion. The mean of maximum values of displacements and hydrodynamic pressures are compared with the deterministic analysis results.

Comparison of stochastic and deterministic dynamic responses of gravity dam–reservoir systems using fluid finite elements

In this paper, stochastic and deterministic dynamic responses of gravity dam–reservoir systems are compared using the displacement fluid finite elements. For stochastic dynamic analysis of gravity dam–reservoir systems, variable-number-nodes two-dimensional fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a general-purpose computer program, which is used for stochastic dynamic analysis of solid systems, STOCAL. The Sarıyar concrete gravity dam, constructed in Turkey is selected for numerical example. The S16E component recorded at Pacoima dam during the San Fernando Earthquake in 1971 is used as a ground motion. Displacements and hydrodynamic pressures occurring on the upstream face of the dam and stresses occurring on the dam section are calculated by using stochastic and deterministic methods and compared with each other.

Implementation of a Level Set Interface Tracking Method in the FIDAP and CFX-4 Codes

We present a streamline-upwind–Petrov-Galerkin (SUPG) finite element level set method that may be implemented into commercial computational fluid dynamics (CFD) software, both finite element (FE) and finite volume (FV) based, to solve problems involving incompressible, two-phase flows with moving interfaces. The method can be used on both structured and unstructured grids. Two formulations are given. The first considers the coupled motion of the two phases and is implemented within the framework of the commercial CFD code CFX-4. The second can be applied for those gas-liquid flows for which effects of the gaseous phase on the motion of the liquid phase are negligible; consequently, the gaseous phase is removed from consideration. This level set formulation is implemented in the commercial CFD code FIDAP. The resulting level set formulations are tested and validated on sample problems involving two-phase flows with density ratios of the order of 103 and viscosity ratios as high as 1.6×105.

Numerical study of fluid loading approximations for submerged spherical shells using finite, infinite and boundary element methods

Numerical studies were conducted to compare acoustic fluid loading approximations for submerged spherical shells. Rigid and empty elastic shells submerged in a heavy acoustic fluid and subjected to harmonic excitation were considered. Solutions using boundary elements, infinite elements, and analytical approximations were compared, with special attention to modeling the near-field fluid beneath the infinite elements. In this case, the near-field fluid is typically modeled using fluid finite elements with frequency dependent mesh refinement and radial extent. The spherical shell is modeled in the same manner using shell finite elements for both boundary and infinite element solutions in order to provide a direct comparison of the fluid loading approximations. Convergence studies involving the near-field fluid were performed with emphasis on the effects of meshing parameters, including refinement, mesh grading, and polynomial order of the radial basis functions for p-version fluid finite elements. Results of interest include comparisons of the submerged structural response, focusing on the reactive and resistance parts of the fluid impedance.

A platform for parallel CFD FEM computations

It is a time consuming and very skilful task for researchers or developers in computational mechanics to modify a program, designed for a single processor, to one suitable for parallel computation. This is a serious bottleneck in parallel computation, even though a general-purpose parallel computational library, such as MPI, is applied to this modification. We have developed a parallel matrix solver platform, based on a domain decomposition method, for various numerical schemes such as the finite element method (FEM), the finite difference method and the finite volume method, to accelerate a smooth shift to the realm of parallel computation. Parallel software such as PETSc, Aztec, GEOFEM and ADVENTURE have already been developed, however these systems are more suitable for professionals in parallel computation and not valid for our purpose. In our platform, a user is merely required to call the platform at the stage of stiffness matrix calculation. GMRES and Bi-CGSTAB with several pre-conditioners are used as a basic matrix solver. The option of invoking a Lagrange-multiplier is also included. For partitioning, a fast graph generator for arbitrary elements and an interface with MeTis are provided. Our platform is valid for a variety of hardware, including a single processor based workstation, through the exchange of Makefilein. The effectiveness of our platform is evaluated with several examples in the area of finite element fluid dynamics in this paper.

Applicability of time-average fluid holography for analysis of propagating waves

Numerical procedures for construction of digital patterns of fringes mimicking fluid holograms are developed. Because conventional finite-element fluid analysis techniques are based on the approximation of nodal displacements, conjugate smoothing of the values of volumetric strain is performed in order to obtain realistic holographic images. Two-dimensional fluid oscillations are analyzed using the developed techniques. It is shown that though time-average fluid holography is a powerful optical experimental method for analysis of short-term transient processes and harmonic vibrations, it has rather limited applicability to studying propagating waves.

Numerical study of the extrusion process in cereals production: Part II. Analysis of variance

Extrusion cooking of cereals is a complex process, regarding a wide range of food products (snack-foods, baby-foods, cereals for breakfast and pasta). In this work, an analysis of variance (ANOVA) on the extrusion cooking process for cereals in a co-rotating twin-screw extruder was carried out, using a finite-element fluid dynamic simulation model, to study shear rate, residence time and mixing index inside the extruder, varying temperature, screw rotation velocity, flow rate and extruder geometry. Besides, the significance analysis, carried out in this study, have shown several aspects of the process under investigation: (i) the interdependence between shear rate, screw rotation velocity and screw axis ratio seems very strong; (ii) the significance of the effects on shear rate of the variations of temperature and flow rate appears less meaningful; (iii) the influence on the residence time of the flow rate and screw axis ratio is more meaningful respect to the screw speed and temperature. The numerical simulations have revealed numerous aspects that can be used to improve the extrusion process: the flow temperature can be varied without modifying the gelatinization of material that is mainly influenced by screw rotation velocity and screw axis ratio.

Fluid flow analysis by finite element method using arbitrarily deformed elements (Proposal of the GMSR‐method)

AbstractThe generalized MSR‐method (GMSR‐method) is proposed as a finite element fluid analysis algorithm for arbitrarily deformed elements using the error analysis approach. The MSR‐method was originally developed by one of the authors in our previous research works using a modified Galerkin method (MGM) for a convection–diffusion equation and the SIMPLER‐approach. In this paper, this MGM is developed theoretically in the case of arbitrarily deformed elements using the error analysis approach. In the GMSR‐method, since the inertia term and the pressure term are considered explicitly, only symmetrical matrices appear. Hence, it helps us reduce computational memory and computation time. Moreover, artificial viscosity and diffusivity are introduced through an error analysis approach to improve the accuracy and stability. This GMSR‐method is applied for two‐ and three‐dimensional natural convection problems in a cavity. In the computations at different Rayleigh numbers, it is shown that this method gives reasonable results compared to other research works. Thus, it is found that the GMSR‐method is applicable to thermal‐fluid flow problems with complicated boundaries. Copyright © 2004 John Wiley & Sons, Ltd.

Fluid–structural interactions in the inner ear

This paper presents a finite element fluid–structural interaction model for the lateral semicircular canal system of the inner ear. The endolymph is modeled as a slightly compressible Newtonian fluid and the cupula partition is represented by a linearly elastic solid. The fluid–structural interaction problem is treated rigorously with a strong coupling between the fluid flow and the structural displacements. The time evolution of the endolymphatic velocity and pressure fields and cupular displacement and stress fields are closely examined to reveal the intricate dynamics that takes place in the vestibular system during the caloric irrigation test.

Freedom of Choice

This article focuses on fuel cell vehicle that has a long way to go. Maybe those part electric-powered, part gasoline-burning cars will help clear the way. Computer diagnostic tools, such as computational fluid dynamics and finite element analysis, are helping to uncover the ways in which the various media that make up fuel cell stacks compress and how they respond to bipolar plate stresses, to name but two examples of research. Experimental measurement tools were helping researchers to visualize flow, measure temperatures directly, and understand compression distribution. Fuel cells have not become the simple solid-state devices that were predicted initially. Hydrogen has not become any more readily available than it was five years ago. Bridges weigh little compared with the land masses they ordinarily connect. Hybrids may never reach the sales volume that traditional internal combustion engine cars now enjoy, or that fuel cell cars may one day reach.

Simulation and Design for a Tunable Dispersion Compensator Package

A novel optical model for a tunable dispersion compensator is realized by a deliberate packaging scheme ensuing from intensive interactions of mechanical design, materials science and numerical simulation techniques including computational fluid dynamics and finite element analysis. The compensator is comprised of multiple cascaded single cavity Gires-Tournois etalons, each under independent temperature control. Three critical issues are addressed: etalon temperature uniformity, thermal insulation and optical surface deformation of the etalons. With etalon optical surface deformation minimized and etalon temperature uniformity successfully controlled within a range of /spl plusmn/0.1/spl deg/C, this small (232 /spl times/ 139 /spl times/ 16 mm) compensator achieves extremely low group delay ripple (<2.0 ps), low insertion loss ripple (<0.5 dB, insertion loss <6.3 dB), low polarization dependent loss [(PDL),<0.15 dB] and low polarization mode dispersion [(PMD),<0.7 ps]. The dispersion tuning range is from -700 ps/nm to +700 ps/nm in a dispersion passband of 0.2 nm which is sufficient for 10-Gb/s transmission. Thermal insulation design makes the tuning process take effect within 1 min at maximum power consumption 5 W.

Direct frequency domain analysis of concrete arch dams based on FE-(FE-HE)-BE technique

A FE-(FE-HE)-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by solid finite elements, while the reservoir domain is considered by a combination of fluid finite elements and a three-dimensional fluid hyper-element. Furthermore, foundation rock domain is handled by three- dimensional boundary element formulation. Based on thisrnmethod, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various conditions. Moreover, the effects of canyon shape on response of dam, is also discussed.

Nitsche's method combined with space–time finite elements for ALE fluid–structure interaction problems

We propose a weak method for handling the fluid–structure interface in finite element fluid–structure interaction based on Nitsche's method [Abh. Math. Univ. Hamburg 36 (1971) 9]. We assume transient incompressible Newtonian flow and, for the structure, undamped linear elasticity. For the time-discretization, we use the time-continuous (energy conserving) Galerkin method for the structure, and for the fluid we employ the time-discontinuous Galerkin method. This means that the velocity becomes piecewise constant on each timestep for the fluid, matching the time-derivative of the displacements in the solid which is also piecewise constant over a time step. We formulate the method and report some numerical examples using space–time oriented elements for the fluid in order to mimic Lagrangian or ALE-type simulations.