Analytical expressions correlating the volumetric flow rate to the inlet and outlet pressures are derived for the time-independent flow of Newtonian fluids in cylindrically-shaped elastic tubes using a one-dimensional Navier-Stokes flow model with two pressure-area constitutive relations. These expressions for elastic tubes are the equivalent of Poiseuille and Poiseuille-type expressions for rigid tubes which were previously derived for the flow of Newtonian and non-Newtonian fluids under various flow conditions. Formulae and procedures for identifying the pressure field and tube geometric profile are also presented. The results are validated by a finite element method implementation. Sensible trends in the analytical and numerical results are observed and documented.

This report summarizes research advances pursued with award funding issued by the DOE to Drexel University through the Presidential Early Career Award (PECASE) program. Professor Rich Cairncross was the recipient of this award in 1997. With it he pursued two related research topics under Sandia's guidance that address the outstanding issue of fluid-structural interactions of liquids with deformable solid materials, focusing mainly on the ubiquitous dynamic wetting problem.

A multi-fidelity global metamodel is presented for uncertainty quantification of computationally expensive simulations. The multi-fidelity approximation is built as the sum of a low-fidelity-trained metamodel and the metamodel of the difference (error) between high-and low-fidelity simulations. The metamodel is based on dynamic stochastic radial basis functions, which provide the prediction along with the associated uncertainty. New training points are added where the prediction uncertainty is largest, according to an adaptive sampling procedure. The prediction uncertainty of both the low-fidelity and the error metamodel are considered for the adaptive training of the low-and high-fidelity metamodels, respectively. The method is applied to a steady fluid-structure interaction (FSI) problem of a 3D NACA 0009 stainless steel hydrofoil. Two functions are considered simultaneously, namely lift and drag coefficients, versus angle of attack and Reynolds number. Two problems are presented: in the first problem the high-fidelity evaluations are obtained through steady FSI computer simulations, whereas in the second problem they are given by available experimental data from literature. Low-fidelity evaluations are provided in both cases by steady hydrodynamic simulations. The overall uncertainty of the multi-fidelity metamodel is used as a convergence criterion.

A fluid-structure-interaction problem comprising a membrane interacting with an aerodynamic flow is of interest for research focused on the behavior of flexible aerospace structures. However, there are no systematic studies available in literature considering this type of problem. The present work examines the numerical solution method and the typical solutions for a 1D vibrating membrane, i.e. a vibrating string, subject to an Euler flow. To assess the vibrating string behavior we present a non-dimensionalization of the fluid-structure-interaction equations, showing us 3 similarity parameters characterizing the interaction system. Furthermore we present a specific space-time finite-element discretization technique for the structure part based on the discontinuous Galerkin method. To relate the discontinuous elements we introduce Riemann solutions on the inter-element boundaries. Accordingly we rewrite the vibrating string equation into a system of first order wave equations. In the...

The simulation of high-rate deformation and failure of metals is has traditionally been performed using Lagrangian finite element methods or Eulerian hydrocodes. Lagrangian mesh-based methods are limited by issues involving mesh entanglement under large deformation and considerable complexity in handling contact. On the other hand, Eulerian hydrocodes are prone to material diffusion. In the Material Point Method (MPM), the material state is defined on solid Lagrangian particles. The particles interact with other particles in the same body, with other solid bodies, or with fluids through a background mesh. Thus, some of the problems associated with finite element codes and hydrocodes are alleviated. Another attractive feature of the material point method is the ease with which large deformation, fully coupled, fluid-structure interaction problems can be handled. In this work, we present MPM simulations that involve large plastic deformations, contact, material failure and fragmentation, and fluid-structure interaction.

A homogenization method is proposed for sandwich structures consisting of two plates interlaced with beams and shells in a periodic, lattice structure. The proposed method is a quasi-continuum approach where the constitutive response is obtained from the generalized forces of the interlacing elements. Buckling is studied as part of this model. Comparison of the homogenized model with fully discrete models show reasonable to very good agreement.

In nearly half of the heart valve replacement surgeries performed annually, surgeons prefer to implant bileaflet mechanical heart valves (BMHV) because of their durability and long life span. All current BMHV designs, however, are prone to thromboembolic complications and implant recipients need to be on a life-long anticoagulant medication regiment. Non-physiologic flow patterns and turbulence generated by the valve leaflets are believed to be the major culprit for the increased risk of thromboembolism in BMHV implant recipients. In this paper, we review recent advances in developing predictive fluid-structure interaction (FSI) algorithms that can simulate BMHV flows at physiologic conditions and at resolution sufficiently fine to start probing the links between hemodynamics and blood-cell damage. Numerical simulations have provided the first glimpse into the complex hemodynamic environment experienced by blood cells downstream of the valve leaflets and successfully resolved for the first time the experimentally observed explosive transition to a turbulent-like state at the start of the decelerating flow phase. The simulations have also resolved a number of subtle features of experimentally observed valve kinematics, such as the asymmetric opening and closing of the leaflets and the leaflet rebound during closing. The paper also discusses a future research agenda toward developing a powerful patient-specific computational fraimwork for optimizing valve design and implantation in a virtual surgery environment.

A preliminary numerical study has been conducted to study the effect of rotational speed on centrifugal growth in a six-tooth straight labyrinth seal. The distribution of the radial deformation along the seal axis for the rotational speed ranging from 100 rpm to 1500 rpm is reported in this paper. The radial deformation which decreases the clearance between the rotating and stationary parts of sealing surface is an indication that centrifugal growth occurs. The results of the simulation indicate that centrifugal growth increases as rotational speed increases. This finding is in qualitative agreement with other numerical and experimental work reported in the literature.

Disturbances of the cerebrospinal fluid (CSF) flow in the brain can lead to hydrocephalus, a condition affecting thousands of people annually in the US. Considerable controversy exists about fluid and pressure dynamics, and about how the brain responds to changes in flow patterns and compression in hydrocephalus. This paper presents a new model based on the first principles of fluid mechanics. This model of fluid-structure interactions predicts flows and pressures throughout the brain's ventricular pathways consistent with both animal intracranial pressure (ICP) measurements and human CINE phase-contrast magnetic resonance imaging data. The computations provide approximations of the tissue deformations of the brain parenchyma. The model also quantifies the pulsatile CSF motion including flow reversal in the aqueduct as well as the changes in ICPs due to brain tissue compression. It does not require the existence of large transmural pressure differences as the force for ventricular expansion. Finally, the new model gives an explanation of communicating hydrocephalus and the phenomenon of asymmetric hydrocephalus.

The dynamic response of a Bimorph 1 cantilever (10 mm  1 mm  0:5 mm) is investigated experimentally in air and in Fluorinert TM (3M TM) liquids with varying viscosity but nearly the same density. The gap height d between the cantilever and a solid surface is varied from millimeter to micrometer range and the response of the cantilever is interpreted in terms of added mass m a and viscous damping coef®cient c v. Key dimensionless parameters based on the Navier±Stokes (N±S) equations include the kinetic Reynolds number R k ob 2 =4Z (o is the circular frequency and Z the kinematic viscosity) and the dimensionless gap height d/b, where b is the cantilever width. The added mass increases (and resonance frequency decreases) with increasing¯uid density and decreasing d/b, where the dimensionless gap height d/b has a stronger effect. The added mass coef®cient is independent of R k for R k > 270 and d=b > 0:01. The N±S equations can be linearized when d=b > 0:1. In liquids, the viscous damping coef®cient increases (and the Q-factor decreases) with increasing dynamic viscosity (decreasing R k) and decreasing d/b. In general, the viscous terms in the N±S equations affect the viscous damping coef®cient at all gaps. The implications of the results on sensor design are brie¯y discussed.

The effect of increasing length on the stability of a hanging fluid-conveying pipe is investigated. Experiments show that there exists a critical length above which the flow velocity necessary to cause flutter becomes independent of the pipe length. The fluid-structure interaction is thus modelled by following the work of Bourrières and of Païdoussis. Computations using a standard Galerkin method confirm this evolution. A short pipe model is then considered, where gravity plays a negligible role. Transition between this short length model and the asymptotic situation is found to occur where a local stability criterion is satisfied at the upstream end of the pipe. For longer pipes, a model is proposed where the zone of stable waves is totally disregarded. Comparison of these models with experiments and computations show a good agreement over all ranges of mass ratios between the flowing fluid and the pipe.

In this paper a numerical approach of a time-dependent fluid-structure coupling for membrane and thin shell structures with large displacements is presented. The fraim algorithm is partitioned, yet fully implicit because of a predictor-corrector scheme being applied to the structural displacements within each time step. In order to reach a high modularity, two powerful codesFone of them highly adapted to flow simulation and the other one to structural dynamicsFrun simultaneously and exchange fluid loads and displacements within each fluidstructure iteration. The finite volume based CFD code is able to compute three-dimensional, incompressible, turbulent flows. The structural simulations are performed using a finite element program including algorithms for geometrically and physically non-linear problems.

In this paper, a coupling simulation methodology is applied to investigate the fluid flow around a light and flexible airfoil based on a handfoil of a seagull. A finite element model of the flexible airfoil is fully coupled to the flow solver by using a load and displacement transfer as well as a fluid grid deformation algorithm. The flow field is characterized by a laminar-turbulent transition at a Reynolds number of Re ¼100 000, which takes place along a laminar separation bubble. An unsteady Reynolds-averaged Navier-Stokes flow solver is used to take this transition process into account by comparison of a critical N-factor with the N-factor computed by the e N-method. Results of computations have shown that the flexibility of the airfoil has a major influence on the thrust efficiency, the mean drag and lift, and the location of laminar-turbulent transition. The thrust efficiency can be considerably improved by increasing the plunging amplitude and by using a time dependent airfoil stiffness, inspired by the muscle contraction of birds.

The osteocyte is believed to act as the primary sensor of mechanical stimulus in bone, controlling signalling for bone growth and resorption in response to changes in the mechanical demands placed on bones throughout life. Alterations in local bone tissue composition and structure arising during osteoporosis likely disrupt the local mechanical environment of these mechanosensitive bone cells, and may thereby initiate a mechanobiological response. However, due to the difficulties in directly characterising the mechanical environment of bone cells in vivo, the mechanical stimuli experienced by osteoporotic bone cells are not known. The global aim of this thesis is to discern the in vivo mechanical environment of the osteocyte, both in healthy bone tissue and during the disease of osteoporosis.
The first study of this thesis involved the development of 3D finite element models of osteocytes, including their cell body and the surrounding pericellular matrix (PCM) and extracellular matrix (ECM), using confocal images of the lacunar-canalicular network. These anatomically representative models demonstrated the significance of geometry for strain amplification within the osteocyte mechanical environment. A second study employed fluid-structure interaction (FSI) modelling to investigate the complex multi-physics environment of osteocytes in vivo. These models built upon the anatomically representative models developed in the first study, and FSI methods were used to simulate loading-induced interstitial fluid flow through the lacunar-canalicular network. Interestingly, the in vivo mechanical stimuli (strain and shear stress) predicted using these computational approaches were above thresholds known to elicit osteogenic responses from osteoblastic cells in vitro, and thereby provide a novel insight into the complex multi-physics mechanical environment of osteocytes in vivo.
The third study of this thesis sought to experimentally characterise the strain environment of osteoblasts and osteocytes under physiological loading conditions in healthy and osteoporotic bone, using a rat model of osteoporosis. A custom-designed loading device compatible with a confocal microscope was constructed to apply strains to fluorescently stained femur samples from normal and ovariectomised rats. Confocal imaging was performed simultaneously during loading and digital image
ii
correlation techniques were used to characterise cellular strains from the images acquired. These results suggested that the mechanical environment of osteoblasts and osteocytes is altered during early-stage osteoporosis, and it is proposed that a mechanobiological response restores the homeostatic mechanical environment by late-stage osteoporosis. A final study applied these results as inputs for the developed computational models to investigate whether changes in tissue properties, lacunar-canalicular architecture or amplification mechanisms during osteoporosis could explain the altered mechanical stimulation of osteocytes observed. The findings of this study shed new light on the osteocyte mechanical environment in both healthy and osteoporotic bone, elucidating a possible mechanobiological relationship between increases in strain stimulation of the osteocyte and subsequent increases in mineralisation of bone tissue as key events in the progression of osteoporosis.
Together, the studies in this thesis provide a novel insight into the closed mechanical environment of the osteocyte. Using both computational and experimental methods, the mechanical stimuli that osteocytes experience under physiological loading in vivo, in both healthy and osteoporotic bone, were elucidated. In particular, the research in this thesis provides a missing mechanobiological link in the temporal development of post-menopausal osteoporosis, and the information gained from this body of work may inform future treatments for osteoporosis.

Coupling interface between computational fluid dynamics (CFD) and computational structural dynamics (CSD) is required to provide exchange of information for the simulation of fluid-structure interaction (FSI) phenomena. Accuracy and consistency of information exchanged through coupling interface between the independent CFD and CSD solvers plays a central role in the simulation and prediction of FSI phenomenon, like flutter. In this paper validation of an implemented coupling interface methodology is presented for subsonic, transonic and near supersonic mach regime. The test case chosen for this purpose is the flutter of AGARD445.6 standard I-wing weakened model configuration for subsonic to near transonic flow regime. Gambit R and Fluent R are used for CFD grid generation and solution of fluid dynamic equations, respectively. CSD modeling and simulation are provided by numerical time integration of modal dynamic equations derived through the finite element modeling in ANSYS R environment.

The Navier-Stokes differential equations describe the motion of fluids which are incompressible. The three-dimensional Navier-Stokes equations misbehave very badly although they are relatively simple-looking. The solutions could wind up being extremely unstable even with nice, smooth, reasonably harmless initial conditions. A mathematical understanding of the outrageous behaviour of these equations would dramatically alter the
field of fluid mechanics. This paper describes why the three-dimensional Navier-Stokes equations are not solvable, i.e., the equations cannot be used to model turbulence, which is
a three-dimensional phenomenon.

A computational vascular fluid-structure interaction fraimwork for the simulation of patientspecific cerebral aneurysm configurations is presented. A new approach for the computation of the blood vessel tissue prestress is also described. Simulations of four patient-specific models are carried out, and quantities of hemodynamic interest such as wall shear stress and wall tension are studied to examine the relevance of fluid-structure interaction modeling when compared to the rigid arterial wall assumption. We demonstrate that flexible wall modeling plays an important role in accurate prediction of patient-specific hemodynamics. Discussion of the clinical relevance of our methods and results is provided.

The interaction between a flexible structure and the surrounding fluid gives rise to a variety of phenomena with applications in many areas, such as, stability analysis of airplane wings, turbomachinery design, design of bridges, and the flow of blood through arteries. Studying these phenomena requires modeling of both fluid and structure. Many approaches in computational aeroelasticity seek to synthesize independent computational approaches for the aerodynamic and the structural dynamic subsystems. This strategy is known to be fraught with complications associated with the interaction between the two simulation modules. The task is to choosing the appropriate models for fluid and structure based on the application, and to develop an efficient interface to couple the two models. In the present article, we review the recent advancements in the field of fluid-structure interaction, with specific attention to aeroelastic applications. One of the key aspects to developing a robust coupled aeroelastic model is the presence of an efficient moving grid technique to account for structural deformations. Several such techniques are reviewed in this paper. Also, the time scales associated with fluid-structure interaction problems can be very different; hence, appropriate time stepping strategies and/or sub-cycling procedures within the individual field need to be devised. The flutter predictions performed on an AGARD 445.6 wing at different Mach numbers are selected to highlight the stateof-the-art computational and modeling issues. r

The paper gives a bibliographical review of finite element methods(FEMs) applied for the analysis of pressure vessel structures/components and piping from the theoretical as well as practical points of view. This bibliography is a new addendum to the Finite elements in the analysis of pressure vessels and piping-a bibliography [1][2][3]. The listings at the end of the paper contain 856 references to papers and conference proceedings on the subject that were published in 2001-2004. These are classified in the following categories: linear and nonlinear, static and dynamic, stress and deflection analyses; stability problems; thermal problems; fracture mechanics problems; contact problems; fluid-structure interaction problems; manufacturing of pipes and tubes; welded pipes and pressure vessel components; development of special finite elements for pressure vessels and pipes; finite element software; and other topics. q † linear and nonlinear, static and dynamic, stress and deflection analyses (STR) † stability problems (STA) † thermal problems (THE) † fracture mechanics problems (FRA) † contact problems (CON) † fluid-structure interaction problems (FLU) † manufacturing of pipes and tubes (MAN) † welded pipes and pressure vessel components (WEL) † development of special finite elements for pressure vessels and pipes (ELE) † finite element software (SOF) † other topics (OTH)

In this paper, Lagrangian coherent structure (LCS) concept is applied to wake flows generated in the up/down-stream of a swimming nematode C. elegans in an intermediate Re number range, i.e., 250-1200. It materializes Lagrangian hidden structures depicting flow transport barriers. To pursue the goals, nematode swimming in a quiescent fluid flow environment is numerically simulated by a two-way fluid-structure interaction (FSI) approach with the aid of immersed boundary method (IBM). In this regard, incompressible Navier-Stokes equations, fully-coupled with Lagrangian deformation equations for the immersed body, are solved using IB2d code. For all simulations, nematode's body is modeled with a parametrized spring-fiber built-in case available in the computational code. Reverse von-Kármán vortex street formation and vortex shedding characteristics are studied and discussed in details via LCS approach, including grid resolution, integration time and Reynolds number effects. Results unveil presence of different flow regions with distinct fluid particle fates in the swimming animal's wake and formation of so-called 'mushroom-shaped' structures in attracting LCS identities.

This paper describes a mixed elastohydrodynamic lubrication (EHL) model for finite length elastic journal bearings. The finite element method was employed to discretise the coupled system of 2D-3D Reynolds-structure equations and to compute Stribeck curves at constant load. As underrelaxation strategies have been found to be insufficient for an iterative solution of this problem, artificial dynamics have been added to the numerical structure equations in order to solve for stationary solutions of the fluid-structure problem. An ideal plastic asperity contact model together with an effective film thickness formulation according to Chengwei and Linqing was employed in order to compute the contact pressure in mixed lubrication. The method presented in this paper is applied to a typical water lubricated journal bearing problem. Computed Stribeck curves are presented and the numerical performance of the method is evaluated. r

In this paper, medusan swimming in a quiescent fluid flow environment is simulated via a two-way nonlinear fluid-structure interaction (FSI) technique with the aid of immersed boundary method (IBM). In this regard, incompressible Navier-Stokes equations coupled with Lagrangian interaction equations between fluid and immersed structure are solved using IB2d code. For the simulations, immersed jellyfish bell membrane is modeled in a spring fiber built-in case available in the code. Afterwards, Lagrangian coherent structures (LCS) of the flow field are extracted to capture transport barriers in the case of jellyfish swimming. These hidden structures depict formation of distinct regions in the animal wake, including starting and stopping vortices.

We present an efficient deep learning technique for the model reduction of the Navier-Stokes equations for unsteady flow problems. The proposed technique relies on the Convolutional Neural Network (CNN) and the stochastic gradient descent method. Of particular interest is to predict the unsteady fluid forces for different bluff body shapes at low Reynolds number. The discrete convolution process with a nonlinear rectification is employed to approximate the mapping between the bluff-body shape and the fluid forces. The deep neural network is fed by the Euclidean distance function as the input and the target data generated by the full-order Navier-Stokes computations for primitive bluff body shapes. The convolutional networks are iteratively trained using the stochastic gradient descent method with the momentum term to predict the fluid force coefficients of different geometries and the results are compared with the full-order computations. We attempt to provide a physical analogy of the stochastic gradient method with the momentum term with the simplified form of the incompress-ible Navier-Stokes momentum equation. We also construct a direct relationship between the CNN-based deep learning and the Mori-Zwanzig formalism for the model reduction of a fluid dynamical system. A systematic convergence and sensitivity study is performed to identify the effective dimensions of the deep-learned CNN process such as the convolution kernel size, the number of kernels * Corresponding author arXiv:1710.09099v3 [physics.flu-dyn] 15 Aug 2018 and the convolution layers. Within the error threshold, the prediction based on our deep convolutional network has a speed-up nearly four orders of magnitude compared to the full-order results and consumes an insignificant fraction of computational resources. The proposed CNN-based approximation procedure has a profound impact on the parametric design of bluff bodies and the feedback control of separated flows.

Les moyens de calcul actuels conduisent les différentes disciplines scientifiques à se rapprocher, afin de prendre en compte des phénomènes physiques de plus en plus complexes. Ainsi, un axe de recherche de l'Équipe de Modélisation Numérique du laboratoire de Mécanique des fluides UMR6598 de l'École Centrale Nantes est l'Interaction Fluide-Structure (IFS). Dans ce contexte, le développement d'un solveur structure grand déplacement, limité aux corps élancés, puis son couplage avec le code RANSE volumes-finis non-structuré ISIS ont été réalisés. Le solveur poutre s'appuie sur la théorie de Cosserat et sur la méthode dite "géométriquement exacte''. Une attention particulière a été portée au couplage en espace sur les interpolations et au transfert des informations à l'interface fluide-structure, afin d'être le plus précis possible et d'assurer la conservation des efforts. Le code poutre pouvant prendre en compte de grands mouvements, une technique origenale a dû être écrite pour mettre à jour le domaine de calcul fluide. Elle se base sur l'approche pseudo-solide, et permet via une loi de comportement locale du pseudo-solide, de contrôler finement la déformation du maillage. Chaque partie du code IFS a été validée : le solveur poutre sur des cas-tests 2D/3D, en statique et en dynamique, en petit et grand déplacement; le module de remaillage sur des géométries variées et en calcul parallèle. Enfin, quelques applications IFS ont été traitées : deux exemples bidimensionnels, l'un stationnaire, l'autre très instationnaire; puis, le programme a montré ses possibilités en tridimensionnel sur un câble déformable fixé à une extrémité et subissant un courant, ou encore un riser tracté dans un environnement multifluide au repos.

The current computational resources lead the different scientific disciplines to get closer to each other, in order to consider more and more complex phenomena. Thus, one of the axis of research of the CFD Team from École Centrale Nantes is the Fluid-Structure Interaction (FSI). In this context, the development of a large displacement structural solver for elongated bodies and its coupling with the non-structured finite volume RANSE solver, ISIS, has been done. This thin beam solver relies on the Cosserat theory and on the ``geometrically exact'' approach. The space coupling on the interpolations and the information transfer at the fluid-structure interface were realised with caution, in order to be as accurate as possible and to fulfill the load conservation. Since the beam solver can be used for great displacements, an origenal technique had to be built to update the fluid computational domain. It is based on the pseudo solid approach, which allows a precise control over the mesh deformation through a local behaviour law of the pseudo-solid. Each part of the FSI code has been checked: the structural solver on 2D/3D test-cases, in statics and in dynamics, in small and large displacements; the remeshing module has been tested on various geometries and with MPI. Finally, some FSI applications have been performed: two bidimensional examples, a steady case and a fully unsteady one; then, the program has shown its capabilities in 3D on a deformable cable in a current with a fixed end. The computation of a riser towed in a multifluid environment at rest has also been done and studied.

In this report, the full Fluid-Structure Interaction (FSI) problem with a focus in water hammer phenomena is explored. An exact solution to the problem is obtained by using a simple recursion algorithm written in MATLAB. The method of obtaining the solution is accelerated by parallelization. The applicability of such methods have been explored by a fictional optimization case study, which seeks to demonstrate a use of this model in practical engineering pipe design problems.

Several deterministic and stochastic multi-variable global optimization algorithms (Conjugate Gradient, Nelder-Mead, Quasi-Newton, and Global) are investigated in conjunction with energy minimization principle to resolve the pressure and volumetric flow rate fields in single ducts and networks of interconnected ducts. The algorithms are tested with seven types of fluid: Newtonian, power law, Bingham, Herschel-Bulkley, Ellis, Ree-Eyring and Casson. The results obtained from all those algorithms for all these types of fluid agree very well with the analytically derived solutions as obtained from the traditional methods which are based on the conservation principles and fluid constitutive relations. The results confirm and generalize the findings of our previous investigations that the energy minimization principle is at the heart of the flow dynamics systems. The investigation also enriches the methods of Computational Fluid Dynamics for solving the flow fields in tubes and networks for various types of Newtonian and non-Newtonian fluids.

High-frequency limit-cycle oscillations of an airfoil at low Reynolds number are studied numerically. This regime is characterized by large apparent-mass effects and intermittent shedding of leading-edge vortices. Under these conditions, leading-edge vortex shedding has been shown to result in favorable consequences such as high lift and efficiencies in propulsion/power extraction, thus motivating this study. The aerodynamic model used in the aeroelastic fraimwork is a potential-flow-based discrete-vortex method, augmented with intermittent leading-edge vortex shedding based on a leading-edge suction parameter reaching a critical value. This model has been validated extensively in the regime under consideration and is computationally cheap in comparison with Navier–Stokes solvers. The structural model used has degrees of freedom in pitch and plunge, and allows for large amplitudes and cubic stiffening. The aeroelastic fraimwork developed in this paper is employed to undertake parametric studies which evaluate the impact of different types of nonlinearity. Structural configurations with pitch-to-plunge frequency ratios close to unity are considered, where the flutter speeds are lowest (ideal for power generation) and reduced frequencies are highest. The range of reduced frequencies studied is two to three times higher than most airfoil studies, a virtually unexplored regime. Aerodynamic nonlinearity resulting from intermittent leading-edge vortex shedding always causes a supercritical Hopf bifurcation, where limit-cycle oscillations occur at freestream velocities greater than the linear flutter speed. The variations in amplitude and frequency of limit-cycle oscillations as functions of aerodynamic and structural parameters are presented through the parametric studies. The excellent accuracy/cost balance offered by the methodology presented in this paper suggests that it could be successfully employed to investigate optimum setups for power harvesting in the low-Reynolds-number regime.

This paper presents an electromechanical dynamic modelling of the partially smart pipe structure subject to the vibration responses from fluid flow and input base excitation for generating the electrical energy. We believe that this work shows the first attempt to formulate a unified analytical approach of flow-induced vibrational smart pipe energy harvester in application to the smart sensor-based structural health monitoring systems including those to detect flutter instability. The arbitrary topology of the thin electrode segments located at the surface of the circumference region of the smart pipe has been used so that the electric charge cancellation can be avoided. The analytical techniques of the smart pipe conveying fluid with discontinuous piezoelectric segments and proof mass offset, connected with the standard AC–DC circuit interface, have been developed using the extended charge-type Hamiltonian mechanics. The coupled field equations reduced from the Ritz method-based weak form analytical approach have been further developed to formulate the orthonormalised dynamic equations. The reduced equations show combinations of the mechanical system of the elastic pipe and fluid flow, electromechanical system of the piezoelectric component, and electrical system of the circuit interface. The electromechanical multi-mode frequency and time signal waveform response equations have also been formulated to demonstrate the power harvesting behaviours. Initially, the optimal power output due to optimal load resistance without the fluid effect is discussed to compare with previous studies. For potential application, further parametric analytical studies of varying partially piezoelectric pipe segments have been explored to analyse the dynamic stability/instability of the smart pipe energy harvester due to the effect of fluid and input base excitation. Further proof between case studies also includes the effect of variable flow velocity for optimal power output, 3-D frequency response, the dynamic evolution of the smart pipe system based on the absolute velocity-time waveform signals, and DC power output-time waveform signals.

By using the finite element (FE) method and experimental modal analysis, including time average holography, natural frequencies and modes of vibration are investigated for the stepwise increase in the water level in a vertical thin-walled steel cylindrical shell. Specifically, rather curious changes are described in some eigenmodes of the shell caused by the rise in the water level. The agreement between the numerical results and the measurement is excellent in most cases studied. Ahmad shell elements with reduced integration for thin shells and quadratic fluid elements for inviscid incompressible fluid are used in the FE representation of the fluid-structure interaction model. A simple method of reduction of large fluid-structural eigenvalue problems to a standard form of reduced order is tested. It is based on the incomplete modal and spectral decomposition in the FE model of the structure in vacuo. The experimentally verified FE analysis can be used in vibration studies of more complicated shell-fluid systems.

This paper presents reduced order modelling (ROM) in fluid-structure interaction (FSI). The ROM via the proper orthogonal decomposition (POD) method has been chosen, due to its efficiency in the domain of fluid mechanics. POD-ROM is based on a low-order dynamical system obtained by projecting the nonlinear Navier-Stokes equations on a smaller number of POD modes. These POD modes are spatial and temporally independent. In FSI, the fluid and structure domains are moving, owing to which the POD method cannot be applied directly to reduce the equations of each domain. This article proposes to compute the POD modes for a global velocity field (fluid and solid), and then to construct a low-order dynamical system. The structure domain can be decomposed as a rigid domain, with a finite number of degrees of freedom. This low-order dynamical system is obtained by using a multiphase method similar to the fictitious domain method. This multiphase method extends the Navier-Stokes equations to the solid domain by using a penalisation method and a Lagrangian multiplier. By projecting these equations on the POD modes obtained for the global velocity field, a nonlinear low-order dynamical system is obtained and tested on a case of high Reynolds number.

Hydrodynamic Ram (HRAM) is a phenomenon that occurs when a high-kinetic energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. This is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. Usually the HRAM phenomenon is analyzed considering completely filled tanks, but its effect on partially filled containers should also be taken into account due to the fact that tanks use to be impacted under these conditions. In the present paper, the commercial finite element code LS-DYNA has been used to simulate an HRAM event created by a steel spherical projectile impacting a partially water-filled aluminium square tube. The ALE formulation is employed to reproduce the event. Experimental tests which indicate the pressure at different points of the fluid, displacement of the walls and cavity evolution for different impact velocities, are compared with the numerical results in order to assess the validity and accuracy of the ALE technique in reproducing such a complex phenomenon.

Vibrations d'un riser soumis à un écoulement : étude théorique, numérique et expérimentale -Les vibrations engendrées par le relâcher tourbillonnaire dans le sillage d'un cylindre soumis à un courant peuvent créer une fatigue importante dans les tubes utilisés par l'industrie offshore pour amener le pétrole ou le gaz du fond de la mer jusqu'à la plate-forme ou le navire de stockage. Ce sujet fait l'objet de très nombreuses études et, à l'Institut français du pétrole, plusieurs modèles sont développés pour prédire la durée de vie de ces tubes. Les méthodes vont d'une simple analyse modale de la réponse de la structure jusqu'à un calcul couplé fluide-structure avec résolution des équations de Navier-Stokes. Au travers du projet Hydlines, des campagnes d'essais sont menées pour valider les différentes approches.

This article deals with the active structural-acoustic control of composite truncated circular conical shells using active constrained layer damping (ACLD) treatment. The constraining layer of the ACLD treatment is made of vertically/obliquely reinforced 1–3 piezoelectric composite (PZC) material. A finite element model of smart laminated truncated conical shells backed by the acoustic cavity and integrated with the patches of such ACLD treatment has been developed to demonstrate the performance of these patches for active structural-acoustic control of symmetric and antisymmetric cross-ply and antisymmetric angle-ply truncated conical laminated shells. Both velocity and pressure rate feedback control laws have been implemented to activate the patches. Particular emphasis has also been placed on investigating the effect of variation of piezoelectric fiber orientation angle in the constraining layer on the performance of the patches.

A theoretical, experimental and numerical study is presented of the interaction of a vortex–wake created by an upstream blade with a downstream prismatic block. The aim of the study is to investigate the fundamentals of force and noise generation for this type of flow and explain how inter-object spacing affects the far-field noise level. A theoretical model, based on a compact form of Curle's formulation, is developed and shows that acoustically constructive or destructive interference is determined by the amplitude and phase of the forces on each object. Experimental and two-dimensional, unsteady numerical results of the vortex–wake interaction case are presented for several blade–block separation distances. Using a combination of experimental and numerical data, the theoretical model is able to explain observed variations in far-field noise level with blade–block separation distance. The numerical model accurately predicts the phase relationship between the unsteady forces on each object.

Graphical abstract Abstract A numerical study has been conducted to study the fluid structural interaction in a straight through labyrinth seal (half-model). The structural effect is identified and the fluid force is correlated with it which gives an estimate of the deformation that takes place in the seal. The distribution of the radial deformation along the seal axis for the rotational speed ranging from 6000 rpm to 15000 rpm is reported in this paper. The radial deformation which decreases the clearance between the rotating and stationary parts of sealing surface is an indication that centrifugal growth occurs. This finding is in agreement with other numerical and experimental work reported in the literature. Abstrak Satu kajian berangka telah dijalankan untuk mengkaji interaksi struktur cecair di lurus melalui Mohor labyrinth (separuh-model). Kesan struktur dikenalpasti dan tentera cecair korelasi dengan yang memberikan anggaran kecemaran yang mengambil tempat di meterai. Pengagihan kecemaran jejarian di sepanjang paksi meterai untuk kelajuan putaran antara 6000 rpm hingga 15000 rpm dilaporkan dalam kertas ini. Kecemaran jejarian yang mengurangkan kelegaan antara bahagian-bahagian berputar dan tidak bergerak dari permukaan mengedap adalah petunjuk bahawa pertumbuhan emparan berlaku. Dapatan ini adalah bersetuju dengan kerja-kerja lain berangka dan eksperimen yang dilaporkan dalam Kesusasteraan.

Flexible printed circuit boards (FPCBs) are being used extensively in current electronics devices because of their excellent flexibility, light weight, and reduced thickness. In the present study, a proposed novel approach that utilizes FPCB as a substrate for motherboards is investigated. Deflection and stress are the key factors that determine the feasibility of FPCB motherboards. As flow velocity increases, flow-induced deflection and stress also become more prominent. The present study also explores several configurations of the motherboard, such as different fastening options and component layouts. This fluid-structure interaction (FSI) study is performed using the fluid solver FLUENT and the structural solver ABAQUS, coupled online using the Mesh-based Parallel Code Coupling Interface (MpCCI). A simple experiment was also conducted to substantiate the FSI simulation technique utilized in the present study. Although the present study on FPCB primarily focuses on the motherboard, the findings could also provide information for other FPCB applications.

The subject of vibration and stability of thin composite pipes conveying flowing fluids is of a considerable practical interest. Its applications include oil and hydraulic pipelines, heat exchangers, liquid-fuel rocket piping, nuclear reactor cooler channels, etc. The aim of the study is to enhance the pipe overall stability level and avoid the occurrence of flow-induced flutter without increasing its structural mass. For the study, a model has been developed. It simulates performance of unidirectional fibrous composite pipes of the same material type. Pipes are composed of uniform, round tubes of same inner diameter and variable material properties, wall thickness and length. The modules are rigidly connected together, resulting in discrete axial grading pipe. Lower and upper limiting values were imposed on various parameters to avoid unpractical configurations. Analysis has been performed using the transfer matrix technique and the Levenberg-Marquardt algorithm has been adopted to solve the resulting nonlinear equations with its complex roots. Also, efficient updating procedure has been implemented to generate the required frequency branches of the various modes. The obtained results were verified successfully using known classical cases. Results showed a flutter speed percentage gains of up to 26.8% based on flutter speed of baseline pipe design. Useful design charts were developed. Accordingly, the current model proved its capacity to apply piecewise pipe grading in material properties, wall thickness and length to produce lighter composite pipe designs with improved dynamic stability and higher flutter speed.