bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Fluidelastic Vibrations of Heat Exchanger Tubes With Loose Supports
Authors: Hassan Marwan
Published: July 2008

Fluidelastic instability is regarded as the most complex and destructive flow excitation mechanism in heat exchanger tube arrays subjected to cross fluid flow. Several attempts have been made for modelling fluidelastic instability in tube arrays in order to predict the stability threshold. However, fretting wear prediction requires a nonlinear computation of the tube dynamics in which proper modelling of the fluid forcing function is essential. In this paper, a time domain simulation of fluidelastic instability is presented for a single flexible tube in an otherwise rigid array subjected to cross fluid flow. The model is based on the unsteady flow theory proposed by Lever and Weaver [1] and Yetisir and Weaver [2]. The developed model has been implemented in INDAP (Incremental Nonlinear Dynamic Analysis Program), an in-house finite element code. Numerical investigations were performed for two linear tube-array geometries and compared with published experimental data. A reasonable agreement between the numerical simulation and the experimental results was obtained. The fluidelastic force model was also coupled with a tube/support interaction model. The developed numerical model was utilized to study a loosely-supported cantilever tube subjected to air flow. Tube-to-support clearance, random excitation level, and flow velocity were then varied. The results indicated that the loose support has a stabilizing effect on the tube response. Both rms impact force and normal work rate increased as a result of increasing the flow velocity or the support radial clearance. Contact ratio exhibited a sharp increase at a flow velocity higher than the instability threshold of the first unsupported mode. In addition, an interesting behaviour has been observed, namely the change of tube’s equilibrium position due to fluid forces. This causes a single-sided impact. At a higher turbulence level, double-sided impact conditions were dominant. The influence of these dynamic regimes on the tube/support parameters was also addressed.
Fluid-Elastic Vibration of Cross-Shaped Tube Bundle in Mixed Cross and Parallel Flow: Measurement of Gap Flow Velocity and Vibration Characteristics
Authors: Inada Fumio , Nishihara Takashi , Mizutani Jun
Published: July 2008

A cross-shaped control rod guide tube bundle is proposed for the lower plenum structure in the next-generation LWR, ABWR-II. In our previous studies, we measured the local fluid excitation forces acting on a cross-shaped tube bundle as well as the self-excited vibration characteristics in pure cross flow in water tunnel tests. In the reactor conditions, the flow field around the tube bundles contains mixed cross and parallel flow components. In this study, water tunnel tests under mixed cross and parallel flow conditions were preformed to understand the influence of the balance of parallel and cross flow components on vibration response. The distributions of the flow direction and flow velocity in the gap between the adjacent tubes were measured with circular Pilot tubes in detail. It was found that the critical flow velocity of self-excited vibration was not influenced by the parallel flow component, but depended only on the cross flow component.
Effect of Parallel Plane Walls on Vortex-Induced Oscillations of a Cylinder
Authors: Kato Shuichi , Aritomi Shunsuke , Maruyama Shinichi , Yoshizawa Masatsugu
Published: July 2008

This paper addresses the vortex-induced oscillations of a spring-supported cylinder in a narrow channel. The characteristics of the two-dimensional laminar fluid flow in a narrow channel deeply depend on the oscillations of the cylinder. The main purpose of this paper is to clarify the effects of channel walls on the nonlinear interaction between transverse oscillations of the cylinder and the unsteady fluid flow in a narrow channel. The following two problems were investigated in order to estimate the effect of channel walls. First, the spring stiffness, which supports a cylinder in a narrow channel, is varied. As the spring stiffness becomes weak, the time history of the cylinder displacement includes not only an oscillating component (A.C.), but also a constant component (D.C.). The numerical results indicated that the D.C. component is generated by viscous force. Second, the frequency and amplitude of the cylinder oscillation and vortex-shedding frequency are measured in and around the lock-in region in case of a blockage ratio w = 2.5. The blockage ratio is the ratio of the channel width to the cylinder diameter. The results in the lock-in region in a narrow channel are different than in the general wall-less lock-in region where such behaviors have never been observed. In this study, the experiments are also performed at Reynolds numbers Re below 200. The cylinder motion and the fluid velocity are simultaneously measured with an angular displacement meter and a PIV (Particle Image Velocimetry) system, respectively. Furthermore, the experimental results are compared with the theoretical results that are obtained from the numerical calculation of the two-dimensional incompressible Navier-Stokes equations.
Experiments on the Planar Lateral Vibration of a Vertical Fluid-Conveying Pipe With an End Mass
Authors: Ajiro Junji , Yamashita Kiyotaka , Motoki Arata , Yoshizawa Masatsugu
Published: July 2008

This paper experimentally examines lateral vibrations of a cantilevered pipe that is hung vertically with an end mass and conveys fluid with a flow velocity that is entirely constant. It is well known from linear stability theory that when the velocity of a fluid exceeds a certain value, a certain characteristic mode of pipe vibration becomes unstable. Moreover, higher modes of pipe vibration become unstable simultaneously with increasing flow velocities. We are interested in the case in which two-frequency oscillation occurs in the pipe involving the above two unstable modes at higher flow velocities. This phenomenon will be called mixed mode flutter. This phenomenon for a cantilevered pipe is essentially different from the cases of a pined-pined or clamped-clamped pipe with two marginal modes. In these cases, only the higher mode of the pipe vibration becomes unstable while the lower mode becomes stable at much higher flow velocities. Experiments were conducted with a silicon rubber pipe conveying water. The planar behaviors of the vertical fluid-conveying pipe with an end mass were observed using an image processing system that is based on the images captured by two CCD cameras. As a result, lower mode flutter, unstable mixed-mode flutter and also higher mode flutter were experimentally confirmed for the cantilevered pipe. Furthermore, the above phenomena are discussed using the basic equation of nonlinear planar lateral vibration of a vertical fluid-conveying pipe with an end mass from the viewpoint of nonlinear dynamics.
The Influence of a Convergent Nozzle on the Flow Field of Downstream Located Mild Stenoses
Authors: Papaioannou T. G. , Christofidis Ch. Ch. , Mathioulakis D. S.
Published: July 2008

The scope of this study is the investigation of the influence of a convergent nozzle type stent on the flow field of one or two downstream located 50% stenoses. Both steady and unsteady inlet flow conditions are examined. The flow is predicted using the commercial code FLUENT, and the recirculation zones downstream of each stenosis are examined through flow visualization in a suitable experimental setup.
Estimation of Non-Linear Damping Parameters in a Normal Triangular Array Subject to Fluidelastic Instability
Authors: Meskell Craig , Eret Petr
Published: July 2008

The non-linear damping parameters associated with a coupled fluidelastic system have been extracted using the non-linear decrement method. The response of a single flexible tube in a five row normal triangular tube array (P/d = 1.32) was recorded over a range of freestream velocities with air as the working fluid. The structural damping has been set so as to avoid fluidelastic instability. The linear and cubic fluidelastic damping parameters have been obtained. Using these identified quantities, the limit cycle amplitudes for the system at lower structural damping levels have estimated. Good agreement between the predicted values and the experimental data is achieved.
Fluid-Solid Interaction Simulation of Flow and Stress Pattern in Thoracoabdominal Aneurysms: A Patient Specific Study
Authors: Borghi Alessandro , Wood Nigel B. , Mohiaddin Raad H. , Xu X. Yun
Published: July 2008

Thoracoabdominal aneurysm (TA) is a pathology that involves the enlargement of the aortic diameter in the inferior descending thoracic aorta and has risk factors including aortic dissection, aortitis or connective tissue disorders (Webb, T. H. and Williams, G. M. 1999). Abnormal flow patterns and stress on the diseased aortic wall are thought to play an important role in the development of this pathology and the internal wall stress has proved to be more reliable as a predictor of rupture than the maximum diameter for abdominal aortic aneurysms (Fillinger, M. F., et al. 2003). In the present study, two patients with TAs of different maximum diameters were scanned using magnetic resonance imaging (MRI) techniques. Realistic models of the aneurysms were reconstructed from the in vivo MRI data acquired from the patients, and subject-specific flow conditions were applied as boundary conditions. The wall and thrombus were modeled as hyperelastic materials and their properties were derived from the literature. Fully coupled fluid-solid interaction simulations were performed for both cases using ADINA 8.2. Results were obtained for both the flow and wall stress patterns within the aneurysms. The results show that the wall stress distribution and its magnitude are strongly dependent on the 3-D shape of the aneurysm and the distribution of thrombus.
The Natural Vibration of Fluid-Structure Interaction Systems Subject to the Sommerfeld Radiation Condition
Authors: Xing Jing T.
Published: July 2008

A fluid-structure interaction system subject to a Sommerfeld condition is defined as a Sommerfeld system in this paper. It is well known that the natural vibration of a dynamic system is defined by the eigenvalue problem of the corresponding idealized system with no material damping assumed and external forces. From the defined eigenvalue problem, the real natural frequencies and the corresponding natural modes of the system can be derived. What are the characteristics of natural vibrations of a Sommerfeld system? This paper intends to address this problem by investigating three selected fluid-structure interaction systems. The systems chosen involve the solid structures with one, two and infinite degrees of freedom coupling to an infinite fluid domain subject to a Sommerfeld condition, respectively. The governing equations describing these coupled systems are presented using the theory of continuum mechanics. The theoretical solution for each problem is derived and discussed. The analysis demonstrates that a Sommerfeld system undergoing a natural vibration behaves energy dissipative characteristics although there is no material damping in solid and fluid of the system. The natural vibrations of a Sommerfeld system are governed by a complex eigenvalue problem which has only pairs of complex conjugate natural frequencies. The number of the complex conjugate natural frequencies and corresponding natural modes of this Sommerfeld system equals to the number of the degrees of freedom of the dry solid structure in the system and it is independent of the infinite fluid domain. The natural vibration forms of the solid structure in natural vibrations do not satisfy the orthogonal relationship. The findings in this research reveal some common dynamic characteristics of Sommerfeld systems. An approach for the dynamic response analysis of a Sommerfeld system is proposed based on the orthogonal natural modes of the dry structure in the system which is more efficient for engineering analysis.
The Wake of Two Staggered Circular Cylinders
Authors: Hu J. C. , Zhou Y. , Wang H. F.
Published: July 2008

The work aims to study experimentally the flow structure, heat and momentum transport in the wake of two staggered circular cylinders. The cylinder center-to-center pitch ranged from 1.2 to 4.0, and the angle between the incident flow and the direction through the two cylinder axes was between 0° and 90°. In order to characterize the heat transport of this flow, both cylinders were slightly heated so that heat generated could be considered to be a passive scalar. The velocity and temperature fluctuations were measured using a movable three-wire (one X-wire plus a cold wire) probe across the wake and a fixed X-wire, which acted to provide a reference signal. Measurements were conducted at x/d = 10 and 20 and a Reynolds number of 7000, where d is the cylinder diameter and x is the longitudinal distance from the mid point between the cylinders. Based on phase-averaged vorticity contours and sectional streamlines, the flow structure behind two staggered cylinders is classified into five typical patterns. The flow behaviours for each pattern are examined in detail, including its topology, vortex strength, stability and decay rate. The different behaviours between the patterns are further linked to the different initial conditions. The momentum and heat transport are not presented due to limited space.
Vibration Tests With a 1/13-Scaled 3-D Model of the Folsom Dam Tainter-Gate and Its Prediction by Theory
Authors: Anami Keiko , Ishii Noriaki , Knisely Charles W. , Todd Robert V. , Oku Tatsuya
Published: July 2008

This study presents 3-D model gate vibration test results demonstrating violent spontaneous vibrations and validating the basic assumptions made in previously published theoretical analyses. First, the design of a 1/13-scaled 3-D model of Folsom dam Tainter-gate is presented, in which the streamwise natural bending vibration mode of the skinplate, measured in the field vibration tests on the remaining Folsom gate, is shown to be correctly replicated with the aid of FEM simulations. Secondly, in-air and in-water vibration test results with the 1/13-scaled 3-D model are presented, reproducing the intense coupled-mode self-excited vibrations. Thirdly, test results are plotted on a theoretically calculated stability criterion diagram to confirm the validity of the theoretical analysis. Finally, the intense dynamic instability of the Folsom gate, which could have caused its failure, is presented.
The Interactive Dynamic Behaviour of an Air-Liquid-Elastic Spherical Tank
Authors: Xiong Y. P. , Xing J. T. , Price W. G.
Published: July 2008

The dynamic behaviour of an air-liquid-elastic spherical tank interaction system is investigated. The tank is fully filled with a non-viscous liquid and air and supported at four equally spaced persitions around the outer shell. The governing equations describing this system are presented. A mixed displacement-pressure finite element method is developed adopting the dynamic pressure in the liquid / air and the displacement in the elastic solid as variables to initiate a numerical model incorporating a substructure-subdomain approach. Numerical simulations are presented based on a developed computer program FSIAP. The natural sloshing frequencies and the corresponding vibration modes of the coupled system are derived. To reveal different interactive mechanisms, four cases are investigated. Namely, 1) liquid sloshing in a rigid tank; 2) air-liquid interactions in a rigid tank; 3) liquid-elastic tank interactions; 4) three phase air-liquid-tank interactions. The numerical results obtained demonstrate the complex coupled behaviour of the system. This study provides information for the design of liquid / gas filled tanks in which structure sloshing behavious is of interest.
Aerodynamic Forces Approximations Calculated With a New Analytical Formulation
Authors: Biskri Djallel Eddine , Botez Ruxandra Mihaela
Published: July 2008

Aeroservoelasticity is a multidisciplinary study of three main disciplines: unsteady aerodynamics, aeroelasticity and servo-controls. Two classical methods are used in the literature to approximate the unsteady generalized forces from the frequency domain Q (k) to the Laplace domain Q(s) and these methods are: the Least Squares LS and the Minimum State MS. In the present paper, we present a new method, called Corrected Minimum State (CMS), based on the Standard MS approximation method. This new CMS method uses an analytical form of the error as function of Laplace variable similar to the analytical form of the aerodynamic forces calculated with the MS method. We applied this new method to an F/A-18 aircraft and we found that the CMS method brings improvements in the approximation results in comparison with the standard MS method. It is shown that use of the CMS method on an F/A-18 aircraft will give better results in terms of convergence speeds and precision than the MS method.
Optimal Swimming Modes of a Homo-Sapien Performing Butterfly-Stroke Kick
Authors: Pitman Mark W. , Lucey Anthony D.
Published: July 2008

This paper outlines the development and application of a computational method that finds the most efficient two-dimensional swimming mode of a human performing fully submerged butterfly-stroke kick at high Reynolds number. The optimal solution of this non-linear problem is found using a Genetic Algorithm (GA) search method where possible solutions compete in a ‘survival of the fittest’ scheme to ‘breed’ the optimal solution. The swimming is modelled using Discrete Vortex Method (DVM) and Boundary Element Method (BEM) computational techniques. The BEM solves for the inviscid flow field around the two-dimensional body while the shedding of vorticies from joints where the curvature is high (ie. knee, waist and ankle joints) generate the vortex structures necessary for propulsion. The motion of the limbs is characterised by a displacement function which includes the possibility for simple harmonic or non-harmonic motion with a ‘rest’ period in the kick. The finite number of joints means that a finite length parameter set can be developed which characterises the motion of the swimming body. This parameter set is fed into the GA to perform the optimisation based on a scoring function. In this case, the scoring function is simply the distance that the body swims in a set amount of time. The objective of the GA is to maximise this score for a set kicking frequency. This method opens a wider possibility for optimisation of a variety of systems that involve fluid-structure interactions, particulary the possibility of optimisation in the non-linear regime of prescribed motion coupled with compliant surfaces (such as rubbery flippers) that could further increase efficiency.
Numerical Simulation for Interaction Problem of Largely Deformed Membrane and Fluid
Authors: Yamada Takahiro , Kayane Tomohiro , Itoh Yoshiaki , Ootsuka Ryuko
Published: July 2008

In this paper, a numerical procedure for interaction problem of largely deformed membrane and fluid is proposed. Numerical computations of deformable structures in viscous flows often encounter numerical instability, which arises from incompatibility of boundary conditions on a fluid-structure interface. In this work, two aspects of compatibility condition including the balance of energy on the fluid-structure interface and the coupling algorithm are discussed and measures to improve attainment of them in numerical procedures are proposed. In this work, a finite difference method with overlapped meshes is employed to solve a fluid problem accurately. For a membrane, a finite element approximation with the energy-momentum method for the temporal discretization is applied to ensure the conservation of energy and unconditional numerical stability. Numerical solutions of these two subsystems are coupled by the block Gauss-Seidel method. Numerical results are given to show numerical properties including stability of the proposed procedure.
Effects of Sensor Shape on Oscillating Pressure Measurements With Wind-Tunnel Test Confirmation
Authors: Wu David W. , Choe Hwang
Published: July 2008

This paper summarizes the effects of the pressure sensor shape on the dynamic oscillating pressure measurements when the pressure wave modulating along the steam/air flow path is to be characterized. In the study presented in the paper, a three-dimensional CFD model of the external flow around the protruding, dome-shaped sensor was developed to evaluate the effects of the sensor shape on the external flow pattern, and the detailed flow patterns were studied with this protruding, dome-shaped sensors and compared with the flow patterns for the flush mounted sensors. Then, a one-dimensional analysis was done to predict that the dynamic pressures measured with the protruding sensor do not require significant correction, and this was later supported by wind tunnel tests. The amplitude of the dynamic pressure measured on the protruding sensor was determined to be ranging from 0 to 8% higher than measured by a flush mounted pressure sensor. The frequency of the pressure wave is not affected by the presence of the protrusion.
Instability of a Cantilevered Flexible Plate in Viscous Channel Flow Driven by Constant Pressure Drop
Authors: Tetlow George A. , Lucey Anthony D. , Balint Tibor S.
Published: July 2008

A new approach for studying the stability of a cantilevered flexible plate positioned within a 2-D viscous channel flow is presented as a representation of the human upper airway. Previous work has used constant inlet velocity conditions, an unrealistic assumption when modelling inhalation. Here we model a constant pressure drop that reflects inspiratory effort. Positioning of the flexible plate within the channel can also be varied. The constant pressure drop is imposed for each time step by computing appropriate inlet velocities. The Navier-Stokes equations are solved using an explicit finite-element method written specifically for the channel geometry within which the fully coupled plate moves. The motion of the plate, driven by the pressure field, is modelled using classical thin-plate mechanics with the addition of a shear-stress induced tension term. The investigation focuses on the motion of the flexible plate (soft palate) as one of the contributors to airway blockage during sleep. It is found that the tension induced by the fluid shear-stress can be significant when the plate is sufficiently flexible. We also demonstrate that imposing constant inlet velocity generates over-predictions of energy transfer between flow and flexible plate. Finally, we show that offsetting the flexible plate within the channel leads to changes in oscillation frequency and significant change to its energy interaction with the fluid flow.
Reduced Models for Chaotic Dynamics of a Fluid-Conveying Pipe
Authors: Sarkar Abhijit , Paidoussis Michael P.
Published: July 2008

A high-dimensional model for chaotic vibration of a cantilever conveying fluid having an end-mass is investigated. The nonlinear partial differential equation describing the oscillations of the pipe is converted into a finite set of coupled nonlinear ordinary differential equation (ODEs) using a Galerkin projection with the uniform cantilever-beam modes as basis. Depending on the parameter range of interest, it turns out that the order of the coupled set of ODEs is much larger (up to 18 degree-of-freedom) in order to obtain a convergent solution. In order to construct a bifurcation diagram with the non-dimensional flow velocity as unfolding parameter, a prohibitive amount of computational effort is necessary in a single-processor (serial) personal computer. To alleviate this computational limitation, such bifurcation diagrams for high-order chaotic system are constructed in parallel computer simulation using multi-threading (i.e. auto-parallelism). A significant computational gain is achieved in terms of time-saving through parallel-processing. The computational gain permits a reliable construction of bifurcation diagrams in the chaotic regime within a reasonable time frame. Subsequently, the efficacy of a reduced-order model based on proper orthogonal mode (POD) is contrasted with the high-dimensional model (with uniform cantilever-beam mode as basis). Numerical results demonstrate the merits and drawbacks of the POD-based bifurcation diagram, depending on the non-dimensional flow-velocity chosen to construct the POD.
Separation Interference Method (SIM) to Reduce Aerodynamic Responses of Structures
Authors: Hayashida Koji , Kubo Yoshinobu , Tanaka Yosuke , Kimura Kichiro , Ikeda Hayato
Published: July 2008

The aerodynamic vibrations of bluff bodies are induced by separation flow from a leading edge of the bodies. Therefore, to suppress the separation from the leading edge is essential to reduction of the aerodynamic response amplitude. The authors developed one method and tried to make clear its suppression mechanism. The method is very simple. By using a plate that is placed to normal to the surface of the body at an optimum position, the separation flow from the leading edge is forced to touch the tip of the plate. The separation flow from the leading edge flows down without enrollment in the wake, then, the aerodynamic responses are reduced. The detail of the method and the reduction mechanism are described in the present paper, taking an instance of a square prism that vibrates within vortex-induced vibration region and galloping region. Both vibrations are suppressed by the method. The method was named by Y. KUBO, one of authors, as Separation Interference Method (SIM).
Shaking Table Tests on a Spherical Tank Mock-Up Provided With Seismic Isolation and Flexible Piping Connections
Authors: Forni Massimo , Poggianti Alessandro , Bergamo Giulia , Gatti Fabrizio
Published: July 2008

The Project INDEPTH (Development of INnovative DEvices for Seismic Protection of PeTrocHemical Facilities), supported by the European Commission, has the objective of developing and applying innovative seismic isolation and/or dissipation systems for critical structures at petrochemical facilities. In the framework of INDEPTH, integrated seismic protection systems have been conceived, developed and tested. They are aimed at protecting liquid-filled structures (product storage, spherical and LNG tanks), with new devices (fiber-reinforced isolators, buckling reinforced braces) specific for each application and new flexible piping couplings, to compensate the displacements resulting from the use of isolation systems. The research program has been focused on the selection of critical structures, the design and manufacturing of the devices, the numerical assessment and the experimental validation through shaking table tests [1–4]. A quantification of technical/economical/safety benefits with respect to the conventional state-of-the-art measures presently adopted and potential application to retrofitting has been performed. This paper describes the validation through shaking table tests of the effectiveness of the isolation systems on a spherical mock-up and the related piping system equipped with flexible joints. Different configurations of the mock-up have been tested, such as: fixed base, isolated base with High Damping Rubber Bearings, Fiber Reinforced Rubber Bearings and Lead Rubber Bearings. Furthermore, each configuration has been tested for three different level of filling to verify the sloshing behavior in the sphere and the effectiveness of the isolation systems at filling levels different from the design one (full sphere).
Calculation of Static and Dynamic Characteristics of Multi Wounded Radial Foil Bearing Based on Leakage Flow Induced Vibration Theory
Authors: Kaneko Shigehiko , Wu Xiaoshan
Published: July 2008

Dynamic pressure type foil bearings are expected to serve as shaft bearings for Micro Gas Turbines (MGT). In this study, in order to establish design guidelines of radial foil bearings, dynamical modeling of multi wounded foil bearing was carried out employing leakage flow induced vibration theory. Taking frictional forces due to attached part of the foil and the protrusion, etc. into consideration, static and dynamic characteristics were analyzed to examine the performance and the stability of radial foil bearings.
Energy Transfer Between an Orbiting Cylinder and Moving Fluid
Authors: Baranyi La´szlo´
Published: July 2008

This paper deals with the numerical simulation of low Reynolds number flow past a circular cylinder in orbital motion. Energy transfer between the incompressible fluid and a circular cylinder forced to follow an orbital path is investigated as a function of ellipticity. Limit cycles were investigated and show that ellipticity can have a large effect on the energy transfer. Sudden changes in state (jumps) were found when energy transfer is plotted against ellipticity. Phase angle was altered by about 180° at the jumps. The effect of direction of orbit and initial conditions was also investigated.
Antiflow-Induced Vibration Structure in Hard Disk Drive
Authors: Hirono Yoshiyuki , Oono Makoto , Sega Masahiko , Nagahiro Shin , Arisaka Toshihiro , Kaneko Jirou
Published: July 2008

To meet market demand for the high data density on the disk of a hard disk drive (HDD), reduction of disturbance causing track misregistration is needed. The main disturbance in HDDs in a server or a desktop PC is flow-induced vibrations caused by airflow due to the disk rotation. Generally, there are two kind of flow-induced vibration (FIV) of the structures inside a HDD. One is in-plane or out of plane vibration of the read/write component, i.e., the carriage. Another is out of plane vibration of the disk. In these experiments, we tried to reduce out of plane vibration of the disk and the carriage by making a simple structural change. The investigation is carried out to clear up a cause of FIV of the carriage. The result showed that the outflow from the disk region is strong and can be the cause of the out of plane vibration of both the disk and carriage. To counteract this fluid force, the plates were put against the disks to prevent wind disturbance. As a result, the flow-induced vibrations of the carriage and the disks were significantly reduced. Based on our results, we designed an anti-FIV structure.
Aeroelastic Dynamics of a NACA 0012 Airfoil in the Transitional Reynolds Number Regime
Authors: Poirel Dominique , Harris Yael , Benaissa Aze´mi
Published: July 2008

The work discussed herein is a focused extension of a series of studies that were carried out at the Aeroelasticity Laboratory of the Royal Military College of Canada in recent years. Initial work revealed the presence of self-excited oscillations over certain ranges of airspeed when a NACA 0012 airfoil was immersed in the laboratory’s wind tunnel and allowed to oscillate freely in both pitch and heave. The range of airspeeds tested corresponded to Reynolds numbers in the low-to-moderate regime. While the aeroelastic apparatus is capable of two-degrees-of-freedom motion, the present work concerns only the motion of the airfoil when it is constrained to rotate in pure pitch. A parametric investigation is presently being undertaken to more fully comprehend the airfoil’s pitch behaviour, specifically the amplitude and frequency of its oscillations which are observed in the following range of chord based Reynolds numbers: 5.0 × 104 ≤ Rec ≤ 1.2 × 105. This paper focuses on the effect of the stiffness of the springs used in the apparatus. Other parameters such as surface roughness, turbulence intensity, temperature and initial conditions are also briefly discussed. In conjunction with the pitch oscillation measurements, preliminary results reveal vortices to be present in the wake. In an attempt to determine the frequency and character of these flow structures, as well as to understand the relationship between the airfoil motion and wake dynamics, hot-wire anemometry measurements have been performed.
Steady and Unsteady Surface Pressure Distributions Around Rectangular Prisms With Sharp Edges at Reynolds Number Up to 2.5×106
Authors: D’Auteuil Annick , Larose Guy L.
Published: July 2008

The commonly-held assumption that the aerodynamics of rectangular prisms with sharp edges are insensitive to Reynolds number is shown to have limitations. Flow reattachment on the top and/or bottom of the prisms can be related to Reynolds number, Re. Steady and unsteady surface pressure measurements were carried out on nine different rectangular prisms for Re from 0.3×106 to 2.5×106 at several angles of attack, in smooth and turbulent flow. It was observed that the reattachment was dependent on parameters such as fineness ratio, edge treatment, angle of attack, turbulence of the oncoming flow and Reynolds number. Permanent reattachment occurred for prisms with fineness ratio of 4 and fluctuating reattachment took place for rectangular prisms with fineness ratio as low as 2.
A Complex 3D Acoustic Induced Vibration of a Low NOx Refinery Boiler
Authors: McKee Robert J. , Pantermuehl Joe , Jarzombek Marlan , Gernentz Ryan , Haveman Doug
Published: July 2008

An increasing number of refinery and other large process steam boilers are being installed with or converted to low NOx combustion. The primary result of low NOx combustion is reduced emissions; however, this type of combustion can also lead to unsteady pressures (pulsation), rumbles, and vibrations of boiler components and walls. This paper reports on an investigation of vibrations that were observed on the walls of a new low NOx boiler during its commissioning. Dynamic measurements and 3D acoustic modeling were used to identify and define the fluid force (acoustic) induced vibration problem and to design baffles to eliminate the specific complex acoustic mode that was causing the vibrations. Vibration measurements were recorded at numerous locations on the exterior walls of the boiler so that variations in magnitude and phase of the wall motions at different locations could be determined. The mode shape of the boiler motion was mapped from this data. Pulsation measurements were made on pressure taps at several locations around the boiler. The pulsation data defined the amplitude and phase relationships of the combustion and flow induced acoustic responses within the boiler. A 3D acoustic model of the boiler was created with internal gas properties including the speed of sound based on temperature distribution within the boiler. The model results were compared to measured data and the complex mode of the troublesome acoustic response was identified. Simple symmetric centerline baffles had been attempted by the boiler supplier without eliminating or reducing the vibrations and noise of the boiler. Based on the complex acoustic mode shape of the pulsation within the boiler as identified by the model results that agreed with field data, specific extended baffles were designed and installed to eliminate the vibrations that had been observed. Smooth operation of the low NOx boiler over a wide range of normal operation not previously obtained was achieved with the new baffles installed. The process of dynamic measurements and 3D acoustic modeling to match field data and confirm the mode shape of acoustic responses within a boiler, as described in this paper, can be used to resolve vibration problems including complex situations that are not solvable by other means.
Non-Hopfian Transonic Flutter
Authors: Bendiksen O. O.
Published: July 2008

A critical analysis of the theoretical foundation of the Hopf bifurcation as a model for transonic flutter is presented. Our objective is to show that certain nonlinear transonic flutter instabilities cannot be described using the Hopf theory. The breakdown occurs because the unsteady aerodynamic forces cannot be linearized without introducing nonuniformities in time or space. Consequently, the Hopf linearization also breaks down, and a uniformly valid Jacobian matrix whose eigenvalues normally determine flutter stability no longer exists. This in turn implies that these flutter instabilities cannot be predicted by formulating and solving a classical linear aeroelastic eigenvalue problem, nor can the Hopf bifurcation serve as a model for describing the corresponding nonlinear flutter boundary.
Numerical Simulation of the Multiple Branch Transverse Response of a Low Mass Ratio Elastically Supported Circular Cylinder
Authors: Willden Richard H. J.
Published: July 2008

The paper presents the results of a numerical investigation of the transverse Vortex-Induced Vibrations of an undamped, low mass ratio elastically supported circular cylinder that was subjected to a uniform flow that resulted in a Reynolds number of 104. The numerical simulations were performed using a two-dimensional Large Eddy Simulation model. The computed cylinder response exhibits three branches; the initial, upper and lower branches. The computed initial and lower branches, which exhibit 2S and 2P modes of shedding respectively, show many similarities to those reported from experiments. However, the computed upper branch, on which a maximum amplitude of response of 0.83D was achieved, shows some dissimilarities to those reported from experiments. The failure to correctly simulate the upper branch response is thought to be due to the high degree of flow three-dimensionality that has been reported to exist on the upper branch.
Galloping Experimental Analysis of Conductors Covered With a D-Section on a High-Voltage Overhead Test Line
Authors: Van Dyke Pierre , Laneville Andre´ , Bouchard Dave
Published: July 2008

This paper presents galloping measurements conducted on a high-voltage overhead test line equipped with three single conductors as well as a second configuration of three conductors interconnected with interphase spacers. The test line consists of three suspension spans and two dead-end spans. To induce galloping amplitudes typical of those encountered as ice is formed on the conductor, a D-section jacketing was added to the conductors in the middle span. Conductor displacement was monitored using two accelerometers on each conductor and two video cameras. Different factors potentially influencing galloping amplitude, such as the mode that is excited, conductor tension, D-section mass per unit length and the wind’s angle of attack have been looked at.
On the Pressure and Force Field on a Circular Cylinder Oscillating in the Lock-In Region at Sub-Critical Reynolds Number
Authors: Zasso Alberto , Belloli Marco , Giappino Stefano , Muggiasca Sara
Published: July 2008

The vortex induced vibration of a rigid cylinder has been studied in the subcritical Reynolds range in terms of motion parameters and also in terms of instantaneous pressure distribution on the cylinder surface. The resulting force field has been analyzed as a function of the fundamental parameters z* (non-dimensional amplitude) and Un (critical velocity ratio) showing a possible systematic modelization of the force component synchronous with the oscillation frequency, responsible for the power input in the lock-in region. The magnitude and the phase of the synchronous force component have been studied analyzing build-up events as well as steady state constant amplitude oscillation events. A very close correspondence has been highlighted among the two different analyzed cases, confirming that a quasi-steady model of the force field is a robust and reliable representation of the flow-cylinder interaction force field. This interaction is responsible for the typical transient build-up oscillations of technical interest. The pressure distribution monitored at different locations along the oscillating cylinder axial coordinate allowed finally to show a direct link between the incoming flow velocity distribution and the correlation characteristics of the vortex shedding force distribution along the cylinder axis.
A Numerical Model to Reproduce Vortex Induced Vibrations of a Circular Cylinder
Authors: Belloli Marco , Diana Giorgio , Resta Ferruccio , Muggiasca Sara
Published: July 2008

This article describes a numerical model to reproduce vortex induced vibrations of a circular cylinder. It consists in a single degree of freedom non linear mechanical system, with characterizing parameters identified on the basis of experimental tests in order to reproduce the main features of VIV, in particular vibration amplitudes as function of wind velocity and the energy introduction by the blowing fluid into the mechanical system.
Vibration Mechanisms of a Heated Rod Due to Subcooled Boiling Flow
Authors: Nematollahi M. R. , Akbari M. H.
Published: July 2008

Vibration characteristics of subcooled boiling flow on thin and long structures such as a heating rod were recently investigated by the authors. The results show that the intensity of the subcooled boiling-induced vibration (SBIV) was influenced strongly by the conditions of subcooling temperature, linear power density and flow velocity. Implosive bubble formation and collapse are the main nature of subcooled boiling, and their behavior are the only sources to originate SBIV. Therefore, in order to explain the phenomenon of SBIV, it is essential to obtain reliable information about bubble behavior in subcooled boiling conditions. This was investigated at different conditions of coolant subcooling temperatures of 25 to 75°C, coolant flow velocities of 16 to 53 cm/s, and linear power densities of 100 to 600 W/cm. High speed photography at 13,500 frames per second was performed at these conditions. The results show that even at the highest subcooling condition, the absolute majority of bubbles collapse very close to the surface after detaching from the heating surface. Based on these observations, a simple model of surface tension and momentum change is introduced to offer a rough quantitative estimate of the force exerted on the heating surface. The formation of a typical bubble in subcooled boiling is predicted to exert an excitation force in the order of 10−4 N.
Comparison of Flow-Induced Vibrations Versus Subcooled Boiling-Induced Vibrations on a Heated Rod in Axial Flow
Authors: Akbari M. H. , Nematollahi M. R. , Hashizume H.
Published: July 2008

There has been a history of operational problems due to vibration-induced failures within those heat exchangers with thin and long structures working under fluid flow and boiling or subcooled boiling heat transfer conditions. During the past three decades the effect of dynamic forces of fluid flow has been considered as the major source of these vibrations, with little attention paid to the effect of subcooled boiling on such vibrations. In order to shed some light on this subject, a comparison of flow-induced vibration (FIV) versus subcooled boiling-induced vibration (SBIV) on a heated rod has been conducted. The results suggest that the SBIV intensity is much stronger than that of FIV in the system under investigation. It also shows that the average vibration intensity increases with increasing the subcooled boiling area.
Effects of Frequency Ratio on the Aerodynamic and Dynamic Properties of Bridge Decks
Authors: Qin X. R. , Kwok K. C. S. , Fok C. H. , Hitchcock P. A.
Published: July 2008

A series of wind tunnel sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency held constant for all the tests. Two 2.9 m long sectional bridge models, one simulating the cross-section of a twin-deck bridge with a gap-width to total chord ratio of about 16% and the other with zero gap-width to approximate a thin plate, were tested to determine whether the effects of frequency ratio are similar for bridge decks with different cross-section shapes. The results of wind tunnel tests suggest that for the model with zero gap-width, the flutter derivatives are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities. However, for the model with a relative large gap-width (around 16%), the flutter derivatives are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the model with a 16% gap-width. The results of this investigation show that the torsional-to-vertical natural frequency ratio is an important structural parameter, which can significantly affect wind-structure interaction.
Human
CHN1
Mutations Hyperactivate α2-Chimaerin and Cause Duane's Retraction Syndrome
Authors: Miyake Noriko , Chilton John , Psatha Maria , Cheng Long , Andrews Caroline , Chan Wai-Man , Law Krystal , Crosier Moira , Lindsay Susan , Cheung Michelle , Allen James , Gutowski Nick J. , Ellard Sian , Young Elizabeth , Iannaccone Alessandro , Appukuttan Binoy , Stout J. Timothy , Christiansen Stephen , Ciccarelli Maria Laura , Baldi Alfonso , Campioni Mara , Zenteno Juan C. , Davenport Dominic , Mariani Laura E. , Sahin Mustafa , Guthrie Sarah , Engle Elizabeth C.
Published: July 2008

Duane's retraction syndrome (DRS) is a complex congenital eye movement disorder caused by aberrant innervation of the extraocular muscles by axons of brainstem motor neurons. Studying families with a variant form of the disorder (DURS2-DRS), we have identified causative heterozygous missense mutations in
CHN1
, a gene on chromosome 2q31 that encodes α2-chimaerin, a Rac guanosine triphosphatase–activating protein (RacGAP) signaling protein previously implicated in the pathfinding of corticospinal axons in mice. We found that these are gain-of-function mutations that increase α2-chimaerin RacGAP activity in vitro. Several of the mutations appeared to enhance α2-chimaerin translocation to the cell membrane or enhance its ability to self-associate. Expression of mutant α2-chimaerin constructs in chick embryos resulted in failure of oculomotor axons to innervate their target extraocular muscles. We conclude that α2-chimaerin has a critical developmental function in ocular motor axon pathfinding.
Tail Reconnection Triggering Substorm Onset
Authors: Angelopoulos Vassilis , McFadden James P. , Larson Davin , Carlson Charles W. , Mende Stephen B. , Frey Harald , Phan Tai , Sibeck David G. , Glassmeier Karl-Heinz , Auster Uli , Donovan Eric , Mann Ian R. , Rae I. Jonathan , Russell Christopher T. , Runov Andrei , Zhou Xu-Zhi , Kepko Larry
Published: July 2008

Magnetospheric substorms explosively release solar wind energy previously stored in Earth's magnetotail, encompassing the entire magnetosphere and producing spectacular auroral displays. It has been unclear whether a substorm is triggered by a disruption of the electrical current flowing across the near-Earth magnetotail, at â¼10
R
E
(
R
E
: Earth radius, or 6374 kilometers), or by the process of magnetic reconnection typically seen farther out in the magnetotail, at â¼20 to 30
R
E
. We report on simultaneous measurements in the magnetotail at multiple distances, at the time of substorm onset. Reconnection was observed at 20
R
E
, at least 1.5 minutes before auroral intensification, at least 2 minutes before substorm expansion, and about 3 minutes before near-Earth current disruption. These results demonstrate that substorms are likely initiated by tail reconnection.