bluuebunny/crossref_metadata_2025_split huggingface dataset:
Symmetric Formulations for Modal Analysis of Internal Fluid Structure Systems
Authors: Ohayon Roger 
Published: March 2022

Abstract
This paper deals with appropriate computational methods for modal analysis of elastic structures containing an inviscid fluid (gas or liquid). These methods, based on Ritz-Galerkin projection using appropriate functional basis, allow us to construct reduced models expressed in terms of physical displacement vector field u in the structure, and generalized coordinates vector r describing the behavior of the fluid. Those reduced models lead to symmetric generalized eigenvalue matrix system involving a reduced number of degrees of freedom for the fluid. More precisely, we construct symmetric matrix models of the fluid considered as a subsystem, by considering the response of the fluid to a prescribed normal displacement of the fluid-structure interface. Two distinct situations are analyzed, namely linear vibrations of an elastic structure completely filled with a compressible gas or liquid and linear vibrations of an elastic structure containing an incompressible liquid with free surface effects due to gravity. The first case is a structural acoustic problem with modal interaction between structural modes with acoustic modes in rigid motionless cavity. Wall impedance can also be easily introduced in order to take into account fluid-structure interface dissipation, for further forced response studies. The second case is a hydroelastic-sloshing problem with modal interaction between incompressible hydroelastic structural modes with incompressible liquid sloshing modes in rigid motionless cavity, involving an elastogravity operator related to the wall normal displacement of the fluid-structure interface. For the construction of reduced models, the static behavior at zero frequency play an important role. This is why we start from “well-posed” variational formulations of the problem, in the sense that zero-frequency behavior must be well retrieved in the equations. It should be noted that the so-called “quasi-static correction” term plays a fundamental role in the Ritz-Galerkin procedure (error truncation). The general methodology corresponds to dynamic substructuring procedures adapted to fluid-structure modal analysis. For general presentations of computational methods using appropriate finite element and dynamic substructuring procedures applied to modal analysis of elastic structures containing inviscid fluids (sloshing, hydroelasticity and structural-acoustics), we refer the reader to Morand and Ohayon (1995).
Investigation of Boundary Layer Behavior on Single and Tandem Cylinders
Authors: Lee T. , Panagakos A. 
Published: March 2022

Abstract
The boundary layers developing on a single and two tandem circular cylinders were examined using multiple hot-film sensor arrays for Re = 2.4 – 5.1 × 104. Hot-wire and surface pressure measurements were also made to better understand the flow pattern and the evolution of the vortex street. The results show that, by use of the sensor arrays in conjunction with a bank of constant-temperature anemometers, (i) the effects of the upstream cylinder on the boundary layer developing on the downstream cylinder, (ii) the frequency of the vortex shedding, and (iii) the locations of flow separation and reattachment can be determined non-intrusively and simultaneously. These measurement capabilities will provide a practical means for the characterization and manipulation of unsteady flow phenomena.
Numerical Study on Aeroelastic Instability of a Rectangular Cylinder in Heaving Oscillations
Authors: Tamura Tetsuro , Itoh Yoshiaki 
Published: March 2022

Abstract
The unsteady three-dimensional flows around a forced-oscillating or freely oscillating rectangular cylinder are numerically simulated by means of the direct finite difference method without any turbulence model. We discuss the accuracy of the present method for prediction of unsteady aerodynamic forces and responses to various dynamic properties. First we examine the aerodynamic forces in case of forced oscillation with D/B = 2 of a rectangular cylinder through the comparison with experiments. Also, in order to understand fundamental behaviors of unstable oscillations of a rectangular cylinder, which is elastically mounted in heaving mode in uniform flow, the effect of various dynamic parameters such as mass ratio, damping ratio or the Scruton number, on aeroelastic instabilities is individually investigated.
Calculation of Vibro-Impact Dynamics of Loosely Supported Rods
Authors: Knudsen J. , Massih A. R. , Johansson L. 
Published: March 2022

Abstract
Vibro-impact dynamics of a loosely-supported rod subject to harmonic and random forces are analyzed. A rod constrained by unilateral contact against springs at contact sites located at different positions is modeled. The beam equations of motion for the rod, with appropriate boundary conditions, are discretized in space by finite element method and in time. The contact forces are computed from the displacements. The model has been used to simulate one span of a rod fixed at one end and loose at the other end. Impact forces, and displacements are calculated as a function of time for different friction coefficients when the rod at one end is subject to sinusoidal or random forces. Lissajous figures and phase plane maps for the system are plotted. Further, the wear rate of the rod is predicted. Some of the predictions are compared with experiments and the results are satisfactory.
Multibody Systems in Nonlinear Waves
Authors: Kral R. , Kreuzer E. , Schlegel V. 
Published: March 2022

Abstract
Almost all offshore structures have to be modeled as multibody systems. Only ships or single pontoons can be modeled as a single rigid body. The dynamic behavior of the multibody system is significantly influenced by fluid-structure interactions. So far, most available methods for analyzing these interactions are restricted to single bodies, small wave amplitudes and body motions, or both.
In the present paper a two-dimensional boundary integral approach with fully nonlinear boundary conditions on the free surface is used to simulate the behavior of elastically coupled floating multibody systems in gravity waves. This method will be applied to analyze the dynamics of two floating bodies moored to a quay.
The results of numerical simulations for selected configurations are shown.
Identification of Fluid Dynamic Coefficients for Multiple Mode Vibrations of a Lightly Damped Rectangular Prism in Cross Flow
Authors: Kerenyi K. , Staubli T. , Drobir H. , Massinger N. 
Published: March 2022

Abstract
An experimental investigation of lightly damped multiple-mode vibrations of a rectangular prism in cross flow will be described. The identification of the fluid dynamic force coefficients is performed by means of a regression analysis (Least-Squares-Procedure) accompanied by online numerical simulation, which allows minimization of errors. Non-linear modelization of the equation of motion is shown, which is needed for stability discussion and to describe the response beyond the stability limit. The fluid dynamic damping will be chosen as the responsible control parameter in the model test for a supercritical Hopf bifurcation.
Fluid-Structural-Acoustical Interactions of a Thin Plate in a Cannel With Flowing Fluid
Authors: Zolotarev I. 
Published: March 2022

Abstract
The dispersion properties of the structural and acoustic waves in the coupled plate-fluid system are presented. The thin elastic plate considered as a simply supported one in the first case and as a part of an unlimited wall of a cannel with flowing fluid in the second case. The linear potential flow theory for inviscid fluid is used. The frequency and modal characteristics are analysed in the range of parameters where the coupling effects between vibration of plate and fluid are either weak or dominant.
The properties of simply supported steel plate interacting with air in cannel for some dimensionless parameters of system was studied by using ANSYS finite element code. As a result of this calculation some dispersion characteristics and fluid pressure distribution in the cannel were obtained.
The frequencies and modal properties of this system as a result of numerical solution (by using ANSYS modelling) are compared with some experimental results.
It is shown that in the fluid-elastic system the strongest acoustic-structural coupling exists if the resonances of acoustic and mechanical systems are sufficiently close. In this case the coupled fluid-mechanical system has two different natural frequencies that are neither pure structural properties nor acoustical. Consequently the fluid-plate arrangement can not be studied separately for the structural and acoustical resonances. Even a light medium can significantly change the spectrum of natural frequencies of a structure. Some expressions for calculation of critical flow velocities are derived.
Flow/Acoustic Interactions for Two Cylinders in Cross Flow
Authors: Fitzpatrick J. A. , Nitti F. 
Published: March 2022

Abstract
The noise generated by two cylinders placed in tandem (i.e. the second in the wake of the first) has been investigated for spacings of 5, 4 & 3 diameters. Measurements of turbulence were obtained between the two cylinders and of fluctuating pressure for the near field region for these cylinder spacings using a microphone with a nose cone. Turbulence levels in the test section were varied using a grid upstream and tests were conducted at different flow velocities and incident levels of turbulence. Although, for a number of cases, up to four peaks related to vortex shedding were evident in the spectrum, most measurements exhibited two peaks, a dominant one at the vortex shedding frequency with a secondary peak at twice this value. The measurements show that the vortex noise is strongest at the mid point between the cylinders and at the rear cylinder with levels of 130 dB. The harmonic component was strongest at the downstream cylinder where peak values of 110 dB were obtained.
Three Dimensional CFD-Analyses of Tube Vibrations Induced by Cross Flow
Authors: Kassera Volker 
Published: March 2022

Abstract
A three dimensional CFD code is applied to the analysis of a single elastically mounted tube in cross flow. The unsteady Navier-Stokes equations are solved in a finite volume mesh with a differential Reynolds-Stress model for turbulence. The tube is supported at both ends by a spring and dashpot system in the cross-flow direction. Fluid forces, tube acceleration, tube velocity and tube displacements are computed after each time step due to the actual flow field. The results for rigid and vibrating tubes are analyzed and compared with experimental data given in the literature. Particular attention is given to the influence of vibration amplitude on the correlation length. In the conclusions the lack of models is discussed critically as well as the aspects of computation time. Suggestions are given for improvement and extension of the model to cover multiple tube rows and tube bundles.
A Time Domain Solution of Fluid-Elastic Instability in Steam Generator Tubes
Authors: Brenneman B. , Gurdal R. J. 
Published: March 2022

Abstract
Because of the gaps between the tubes and support plates, the method of solving flow-induced vibration and wear problems in steam generators must involve nonlinear dynamics and the time domain solution of the differential equations. This paper presents several innovations that make the solution practical for today’s personal computers. The method was used to calculate the critical velocity, and the responses and normal work-rates at critical locations on a tube in a commercial steam generator. In the particular steam generator considered, the critical velocity was found to be insensitive to the tube-to-support plate clearances. Also, if turbulence is the only excitation mechanism, the normal work-rate (and hence the wear-rate) decreases with an increase of the tube-to-support plate clearance. However, in the presence of turbulence and the proposed fluid-elastic mechanism, the normal work-rate increases with the tube-to-support plate clearance, even though the cross-flow velocity remains below the critical velocity.
Flow Periodicity and Acoustic Resonance in Parallel Triangle Tube Bundles
Authors: Oengören Abdullah , Ziada Samir 
Published: March 2022

Abstract
Parallel triangle tube arrays with pitch ratios in the range of 1.2 to 4.2 have been tested at Reynolds numbers up to 90000 to investigate the vorticity shedding and acoustic resonance mechanisms. The tests included measurements of the pressure fluctuations on the tubes and on the test section wall, as well as extensive flow visualisation and hot film measurements of the unsteady flow activities.
Three different components of flow periodicities have been observed. The flow periodicity with the highest Strouhal number (S3) is caused by a shear layer instability and is the weakest component. The S2 component is associated with small scale vortex shedding at the first row. The third component has the lowest Strouhal number (S1) and is the strongest. It is generated by large scale, alternating vortex shedding at deeper rows, and it becomes dominant at all rows at high Reynolds numbers.
For tube arrays with pitch ratio less than 3.4, the onset of acoustic resonances could not be related to the natural flow periodicities mentioned above. This behaviour is in contrast with that of normal triangle arrays, but similar to the acoustic behaviour of in-line arrays. The similarity with in-line arrays seems to stem from the fact that both arrays allow the flow to proceed along free flow lanes between the tube columns, resulting in a similar acoustic resonance mechanism. Strouhal number charts for the natural vorticity shedding and the onset of acoustic resonances have been developed.
Tube Rupture in High Pressure Heat Exchangers
Authors: Goyder H. G. D. 
Published: March 2022

Abstract
A high pressure heat exchanger may have a gas at 100 to 400 bar inside the tubes and cooling water at 20 bar outside the tubes. If a tube ruptures the high pressure gas is released into the water and the pressure quickly rises within the shell. The shells of these heat exchangers may only be capable of withstanding relatively low pressures and a level of safety is achieved by providing bursting disks and pressure relief systems. However, such pressure relief systems do not act instantaneously. The problem is to determine if the rapid pressure rise that follows a tube rupture can rupture a shell before the pressure relief system can act to vent the pressure.
Flow-Induced Vibration Failure in a Steam Condenser and its Successful Redesign
Authors: Escoe A. Keith 
Published: March 2022

Abstract
This paper is a study of an inadequate FIV design of a steam condenser. The condenser failed because of lack of tube support baffles. The flow distribution varied widely at different parts of the exchanger. The vibration assessment based on conventional technology showed the exchanger experiencing both fluidelastic instability and turbulence buffeting. The exchanger failed within the first six months of operation, which would suggest FEI as the mechanism of failure. A consulting firm came in and added stakes within the top portion of the tubes. The FIV steadily got worse over a period of twelve years, as operations increased the shell side flow velocity. The increased velocity and leaks suggested low cycle fatigue failures typical of turbulence buffeting. What makes this study interesting is the long unsupported length of the tubes resulted in very low natural frequency of the tubes and tube collisions. The study of tube collisions and the consequences unravel a unique situation. Numerous attempts were made to correct the problem, but were marginally successful. The final and successful “fix” was a new rod baffle design. This design differed from the classical rod-baffle design, because of the large diameter (20 ft). The magnitude of the diameter normally limits the rod baffle design. Modifications of the rod baffle design were to compensate the flexibility of the long length of the tube support rods. This paper will discuss these modifications, showing the corresponding FIV computations, using finite element studies of the tubes and a new FIV software package. This paper will be a unique study of the failure and successful fix of a FIV failure.
Flow-Induced Wear in Steam Generator Tubes: Prediction Versus Operational Experience
Authors: Au-Yang M. K. 
Published: March 2022

Abstract
Many nuclear steam generators have accumulated more than ten effective-full-power-years of operation. Eddy-current inspections revealed that a number of these steam generator tubes, notably those located in high local cross-flow regions, have indications of wear at some support plate elevations after five to ten years of effective-full-power operations. In the last five years, a number of technical papers on non-linear tube bundle dynamics has been published to address the effect of tube and support plate interactions. At the same time, test data relating wear and tube wall thickness losses for different material combinations and different support plate geometries became available. Based on the available data in the literature, as well as data obtained in the author’s affiliation, this paper assesses the cumulative tube wall wear after 5, 10 and 15 effective-full-power years of operation of a typical commercial nuclear steam generator, using different wear models. It is hoped that this study will shed some light on the probable mechanism that caused the observed wear in today’s operating nuclear steam generators.
Active Feedback Control of Combustion Oscillations
Authors: Ziada Samir , Graf Hans R. 
Published: March 2022

Abstract
Combustion oscillations are excited by a feedback mechanism which results from the coupling between the flame instability and an acoustic resonance mode of the combustion chamber. The most important event of this mechanism is believed to be the upstream feedback from the acoustic resonance to the initial region of the flame, where new disturbances are generated. A control system has been implemented into a household burner to counter act this upstream feedback. This is achieved by means of pulsating either the fresh air for combustion or the fuel. The actuators are activated by the signal of a sensor measuring the pulsation inside the combustion chamber. Combustion oscillations of this burner have been eliminated altogether, without destabilising other acoustic modes, resulting in 35 dB reduction in the amplitude of pressure pulsations.
Fluid-Elastic Force Measurements Acting on a Tube Bundle in Two-Phase Cross Flow: Fluid-Elastic Forces Acting on the Oscillated Tube and Tubes Surrounding the Oscillated Tube
Authors: Inada Fumio , Kawamura Koji , Yasuo Akira 
Published: March 2022

Abstract
Fluid-elastic forces acting on a square tube bundle (P/D = 1.42) in air-water two-phase cross flow were considered experimentally. A tube in the tube bundle was oscillated in the direction perpendicular as well as parallel to the two-phase flow, and fluid elastic forces acting on the oscillated tube as well as tubes surrounding the oscillated tube were measured. Measured fluid elastic forces were separated into coefficients of acceleration, velocity, and displacement of the oscillated tube, and the coefficients were nondimensionalized with two-phase mixture characteristics, which were obtained using the drift-flux model. It was found that the fluid elastic force coefficients could collapse very well as a function of void fraction and/or nondimensional gap velocity. These coefficients were used to estimate the critical gap velocity of fluid elastic vibration. The results agreed qualitatively with previous experimental results of Nakamura et al. (1986a,b).
Fluid-Structure Interaction in Hydraulic Networks
Authors: Bouabdallah Saïd , Massouh Fawaz 
Published: March 2022

Abstract
In this study, we consider the fluid-structure interaction in hydraulic networks, with a simplified representation of the structure thanks to the Timoshenko beam theory. This allows us to write the coupled equations which represent both the fluid flow and the structure deformations effects. These equations are solved by the method of characteristics. This last method involves different kinds of characteristics.
In this paper we consider only the longitudinal mode of propagation, which the pipe undergoes in traction and compression. In this case two families of compatibility equations with different characteristic paths must be solved together. For the computation a numerical scheme with a reach-back time interpolation will be used.
Coupled and Uncoupled Bending-Torsion Responses of Twin-Tail Buffet
Authors: Kandil Osama A. , Sheta Essam F. 
Published: March 2022

Abstract
The effect of coupled and uncoupled bending and torsion modes on flexible twin-tail buffet is considered. This multidisciplinary problem is investigated using three sets of equations on a multi-block grid structure. The first set is the unsteady, compressible, full Navier-Stokes equations which are used for obtaining the flow-filed vector and the aerodynamic loads on the twin tails. The second set is the coupled aeroelastic equations which are used for obtaining the bending and torsional deflections of the twin tails. The third set is the grid-displacement equations which are used for updating the grid coordinates due to the tail deflections. The configuration is pitched at 30° angle of attack and the freestream Mach number and Reynolds number are 0.3 and 1.25 million, respectively. Keeping the twin tails as rigid surfaces, the problem is solved for the initial flow conditions. Next, the problem is solved for the flexible twin tails responses due to the unsteady loads produced by the vortex breakdown flow of the delta-wing leading-edge vortex cores. The configuration is investigated for the effect of coupled and uncoupled bending and torsion modes using two different separation distances of the twin-tail; the inboard and the outboard positions.
Parametric Vibration of Elastic Cavitating Wing in Unsteady Flow
Authors: Kovinskaya S. I. , Amromin E. L. 
Published: March 2022

Abstract
A two-dimensional unsteady potential flow outside an elastic partially cavitating wing is analyzed numerically by using the Birnbaum equation on hydrofoil chord and the Lagrange-Cauchy integral on the cavity. An angle of attack has a small periodic perturbation, and cavity thickness and length have got perturbations too. Wing vibration is considered as vibration of a variable thickness beam with two clamp bolts near the beam center. A mono-frequency flow perturbation induces mono-frequency flexural vibration of a non-cavitating wing, but the vibration of a cavitating wing is multy-frequency one, and a spectrum of a cavitating wing response can depend on an amplitude of the incoming flow perturbation.
Numerical simulation of NACA-16009 hydrofoil vibration was made for various free-stream speeds, module of elasticity, fluid and wing densities, and as a result, three frequency bands of a vibration increase are found. The low-frequency band is connected with a cavity volume oscillation. There is a considerable effect of cavity length, therefore the cavitation number influences on vibration as a parameter. The high-frequency band is connected with elastic resonances of wing. Besides, resonance-like frequencies were found in the middle band. This phenomenon has not a dependence on cavity dimensions and wing elasticity, but appears as a result of an interaction between hydrodynamic damping and media inertia forces.