bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Two Methods to Measure the Frequency-Wavenumber Spectrum of the Wall Pressure Field Beneath a Turbulent Boundary Layer
Authors: Giovannelli G. , Hespeel D. , Forestier B. E. , Pognant M. 
Published: January 2022

Abstract
The wavevector-frequency spectral estimation of wall pressure fluctuations by means of multiple Fourier transform processing of multi point data is discussed. This paper compares two methods to estimate the ω-k spectrum. In the first method, fluctuating pressure field measurements are made synchronously. In the Wills (1970) method the fluctuating pressure data are issued from two movable probes. The spectral level at low wavenumbers has been previously evaluated by Iddir (1997) and Giovannelli et al (1997). We use both these experiments in the subconvective domain and the present measurements in the convective part to fit the parameters of Chase’s model (1991) of the wall pressure spectrum. We show that the bias introduced by the discrete Fourier transform estimation on Chase’s model integrated over the transverse wavenumbers is about 5 dB. The addition of Chase’s model and the acoustic excitation of the facility is close to experimental frequency-wavenumber spectral densities. The Maximum Likelihood Method is also performed on the pressure data and on the model.
Wavenumber-Frequency Spectrum Measurement of Wall Shear Stress Fluctuations Beneath a Planar Turbulent Boundary Layer
Authors: Hespeel D. , Giovannelli G. , Forestier B. E. 
Published: January 2022

Abstract
The majority of past and recent works on the wall pressure spectrum of a turbulent boundary layer considers that the wall shear stress effects are negligible. To estimate the contribution of the shear stress dipoles to the wall pressure generation, instantaneous fluctuations of streamwise wall shear stress have been measured using hot-element probes in a planar turbulent boundary layer. Considering various factors such as heat loss to the probe substrate, frequency response of the probes, spanwise averaging and length to diameter ratio of the heated element, the wall shear stress frequency spectra have been studied and the measured relative intensity τrms/τ¯=34% reevaluated to 40%. The wall shear stress correlations show a lower convection velocity and a greater coherence loss than for wall pressure fluctuations. The difference between the wall pressure and the wall shear stress wavenumber-frequency spectra is about 21 dB at the convective maxima and reduces to a few dB at the low wavenumbers.
Subjective Evaluation of the Noise at the Operator’s Ear Position in Earth Moving Machines: A Preliminary Investigation
Authors: Carletti Eleonora , Pedrielli Francesca 
Published: January 2022

Abstract
Laboratory listening tests have been carried out in order to compare the objective parameters commonly used for assessing the noise at the operator’s ear position in the cabin of an earth moving machine, with the subjective perception. The results, although affected by limitations inherently the initial state of the study, show that the parameter that has to be measured in accordance with the international standards currently in force, is not adequate to describe the physical phenomena determining the subjective auditory perception. A further investigation should address the identification of descriptors which better represent the hearing sensation.
Damage Characterization Around a Bullet Hole in Composites
Authors: Baig Zahid I. , Dayal Vinay 
Published: January 2022

Abstract
The ballistic impact of a bullet on thin and thick composites has been studied in this work. Vibration modal analysis was used to ascertain the effect of bullet hole and damage on the change in natural frequency of the laminate. Ultrasound was used to determine the actual extent of damage in the laminate and a quasi-static Finite Element model is employed to determine the development of interlaminar shear stresses and failure in the laminate.
Nondestructive Ply-Layup Identification for Fiber Reinforced Composites Using Genetic Algorithm
Authors: Balasubramaniam Krishnan , Rao Navin S. 
Published: January 2022

Abstract
For multi-oriented layered composite laminates, ply lay-up (stacking sequence) identification is an essential exercise. Lay-up identification falls under the realm of nonlinear inverse problems. Few attempts in this direction are quoted in literature. Of note are the works of Komsky and co-workers [1], where shear wave transmission signals have been used in conjunction with theoretical models or neural networks.
Low Velocity Impact Response of Thin Walled Graphite/Epoxy Cylinders
Authors: Vaidya Uday K. , Jones Michael V. , Kamath Mohan V. , Evans Robert , Vandiver Terry 
Published: January 2022

Abstract
Helical and hoop wound graphite/epoxy (Gr/Ep) composite cylinders have been tested under low velocity impact under simply supported boundary conditions, in two phases. In Phase I, the impact energy levels ranged from 1 to 6 ft-lbs, (1 ft-lb = 1.35J) while in Phase II, the impact energy levels ranged from 35 ft lbs-50 ft lbs. Pre- and Post-impact ultrasonic C-scans have been conducted. The fiber bundles and the winding angle(s) are well resolved through the C-scans. Vibration based NDE has been conducted prior to and after impact to determine modal response of the composite cylinders under a simply supported boundary condition. The modal density of the helical wound cylinders is found to be higher than the hoop wound, while the hoop wound cylinders exhibit higher stiffness. The microstructure of some of the cylinders has been studied by sectioning them at impact locations.
Effect of 3D Reinforcement on the Low-Velocity Impact Response of S2-Glass/Vinyl Ester Composite Laminates
Authors: Hosur M. V. , Vaidya U. K. , Abraham A. , Jeelani S. 
Published: January 2022

Abstract
Due to their inherent weakness in thickness direction, laminated fiber reinforced composites are susceptible to undergo large delamination damage when subjected to transverse loading. Low-velocity impact loading is one such case. Low-velocity impact occurs due to tool-drops during manufacturing, maintenance, and service, runway debris during landing and takeoff and hailstorm. In the current work an effort is made to improve the transverse strength by providing 3D reinforcement in the form of pins and stitching the laminate in thickness direction. Laminates were made of S2-Glass/Vinyl Ester. Specimens of size 3 × 4 inch were subjected to drop-weight impact at energy levels of 20, 31 and 41 Joules. The impacted panels were subjected to vibration tests to determine the stiffness loss through vibration based frequency response function (FRF) measurements. Effect of impact damage on interlaminar shear strength was studied. Results indicate that there is considerable improvement in damage tolerance due to 3D reinforcement.
Effective Dynamical Properties
Authors: Barbone Paul E. 
Published: January 2022

Abstract
We discuss effective dynamical properties of complicated vibratory subsystems. A complicated vibratory subsystem is one in which the resonance structure contains a lot of fine detail. The first part of this paper describes an analogy between the effective vibratory subsystem theory and the effective medium equations used to model composite materials. The second part of this paper presents an example application of the effective vibratory subsystem theory. The effective subsystem theory is used to model a continuous elastic rod. Features of the nonuniform limit ω → ∞ are shown to be reproduced by the effective vibratory sub-system theory.
Rational Interpolation of Sampled Frequency Response Calculations Based on Sophisticated Vibration Theory
Authors: McDaniel J. Gregory , Pierce Allan D. 
Published: January 2022

Abstract
This paper presents a new method for enhancing and extending finite element analyses of structures in the frequency domain. When a finite element model is used to predict the response of a vibrating structure to a time-harmonic excitation, the number of degrees of freedom necessary for a convergent answer scales with the frequency of excitation. At higher frequencies, inversion of the matrix equations of motion for the response vector is computationally expensive and, given a finite amount of computer resources, the response at any particular point on the structure is coarsely sampled in frequency. Direct computation of the modal vectors and natural frequencies is similarly cost prohibitive. The method presented here is intended to increase the frequency resolution of response data over a frequency band by estimating the resonant frequencies which lie in the band and their corresponding modal vectors. These estimates are obtained by inserting into Rayleigh’s Principle a trial modal vector that is a linear combination of the response vectors evaluated at frequencies inside the band. An eigenvalue problem is thereby obtained whose rank is equal to the number of sampled frequencies, which is chosen to be much smaller than the number of degrees of freedom of the structure. The method is demonstrated on a vibrating beam, where it is shown to accurately predict the displacement anywhere over a frequency band which contains four modes.
Numerical Implementation of Inflow/Outflow Conditions for Time-Harmonic Turbomachinery Flows
Authors: Golubev Vladimir V. , Atassi Hafiz M. 
Published: January 2022

Abstract
An efficient numerical scheme is developed to implement the inflow/outflow conditions for unsteady turbomachinery flows. The formulation gives exact non-reflective conditions which can be used with a time-harmonic code for calculating the unsteady flow about blades as well as the acoustic radiation. The method is applied to flows with a mean swirl. Upstream and downstream from the blade row, an asymptotic behavior of the scattered unsteady disturbances is obtained from an eigenmode analysis of the unsteady linearized Euler equations. The inflow/outflow conditions are developed as a filter which selects the physically acceptable modes and thus provides a non-reflective solution throughout the physical space of the annular blade row passage. The direct numerical implementation of the non-reflective conditions may lead to ill-conditioned matrices. An approach is proposed based on matrix factorization which enhances the convergence properties.
Approximations of Power Flow Between Two Coupled Beams Using Statistical Energy Methods
Authors: Tan Y. C. , Castanier M. P. , Pierre C. 
Published: January 2022

Abstract
The present work is concerned with predicting the power flow between two coupled substructures with parameter uncertainties. The power flow is averaged over an ensemble of systems due to the variation of the system parameters. The ultimate aim is to develop a statistical method which may be applied to the mid-frequency range of vibration for a complex structure. The system considered in this paper is two coupled, nominally identical beams on simple supports, with a torsional spring attached at the coupling point. Various methods are presented to calculate the power flow for this system. The Parameter-based Statistical Energy Method (PSEM) is applied to a classical modal solution and a wave solution. The wave approach appears to be more accurate and computationally efficient for this one-dimensional system. The power flow formulated by applying Component Mode Synthesis (CMS) is also presented. It is seen that the CMS formulation may provide a framework for the efficient numerical analysis of power flow in a general complex structure, which may be modeled by the finite element method.
Free Vibration Analysis of Viscoelastic Moving Belts
Authors: Zu Jean W. , Zhang Lixin 
Published: January 2022

Abstract
The nonlinear free vibration of viscoelastic moving belts is studied. Based on the linear viscoelastic differential constitutive law, the generalized equation of motion is derived for a moving belt with geometric nonlinearities. The method of multiple scales is applied directly to the governing equation which is in the form of continuous autonomous gyroscopic systems with weakly nonlinearity. This direct treatment does not involve a prior assumption regarding the spatial solutions. The nonlinear natural frequencies and free response amplitude for autonomous systems are predicted by the perturbation method. The results obtained with the quasi-static assumption and those without this assumption are compared. The effects of elastic and viscoelastic parameters, axial moving speed, and the geometric nonlinearity on natural frequencies and amplitudes of the free response are investigated from numerical examples.
Flow Induced Vibration of Submerged and Inclined Concentric Pipes With Different Lengths
Authors: Wang Xiaodong , Bloom Frederick 
Published: January 2022

Abstract
In this paper, we formulate a mathematical model to study the dynamics of submerged, inclined concentric pipes with different lengths. The governing equations of motion for the inner pipe are derived under small deformation assumptions and with the consideration of gravitational forces, turbulent boundary layer thickness of external flow, fluid frictional forces, and inertia! effects. We obtain discretized dynamical equations using spatial finite difference schemes and calculate the resonant frequencies of a particular pipe system design. In addition, by varying the operating conditions, we identify a few critical parameters pertaining to the proper design of such pipe systems.
Flow Visualization of Oscillating Rectangular Prisms Arranged in Arrays and in Isolation
Authors: Kerenyi K. , Hillisch S. , Drobir H. , Staubli T. 
Published: January 2022

Abstract
This study examines the flow around an isolated rectangular prism as well as around and through an array of equidistant bars. These prisms are excited to oscillate by the flow for certain experimental parameters due to a lightly damped suspension. The experiments with suspension allowing oscillations with mechanically uncoupled, orthogonal degrees of freedom are described, as is the hydrogen bubble technique employed for visualization. A first interpretation of flow images is given starting with the stationary, single bar at various incidence angles of the flow. In a next step the oscillating isolated bar is discussed followed by arrays of five (non-oscillating) and three bars (oscillating). Special focus is put on the influence of the bar spacing and its influence on the excitation of oscillations. It is demonstrated that oscillation can be avoided by appropriately choosing the spacing.
Time-Optimal Input Sequences for Residual Vibration Reduction
Authors: Teo C. L. , Ong C. J. , Xu M. 
Published: January 2022

Abstract
In this article, a method of designing an input sequence to move a flexible structure without residual vibration is presented. The vibration suppression problem is formulated as an optimization problem to find the input sequence that minimizes the time taken for a point-to-point motion. The requirement for zero residual vibration is imposed on the optimization problem as suitable constraints. Other constraints resulting from physical limits existing in the actual system can also be easily incorporated. The only requirement is that the natural frequency and damping ratio of the system be known. However additional robustness constraints can be added to ensure that the solution will be insensitive to slight variations in these parameters. Simulations and experimental results show that the inputs developed here are effective to reduce the residual vibration. In addition, the proposed solution shows a marked insensitivity to errors in natural frequency and damping ratio estimates if the additional robustness constraints are included.
Stability Analysis of Flexible Cam Follower Systems
Authors: Dehghani M. , Hamidzadeh H. R. 
Published: January 2022

Abstract
Dynamic stability of a flexible cam-follower is considered. The shaft-cam-follower assembly is modeled by a single degree of freedom system. In the analysis, transverse and rotational flexibilities of the camshaft along with flexibility of the follower are taken into consideration. This gives rise to a system governed by a linear, second-order, ordinary differential equation with time-dependent coefficients. In general, this class of equations is known as second order Hill’s equation. The time responses of the cam-follower system for an eccentric cam under different rotational speeds are determined. In addition, the stability analysis based on Hill’s infinite determinant is performed, and the effects of operational speed and damping on the stability are determined. For the special case of the cam-follower system that has been considered, it has been found that the system is stable for lower values of the angular speed of the cam. As the speed is increased gradually, a few unstable regions occur. In general, damping shows a significant effect on stabilizing the cam-follower system.
Stability Analysis of Multiple Delayed Resonator Vibration Absorbers
Authors: Jalili Nader , Olgac Nejat 
Published: January 2022

Abstract
This paper is on the use of multiple identical Delayed Resonator (DR), a recently introduced active vibration absorber, in suppressing tonal vibration of multi-degree-of-freedom mechanical structures. The DR methodology forces the conventional mass-spring-damper passive absorbers into marginally stable resonators which absorb all the vibratory energy at their points of attachment. Control forces in the form of proportional acceleration feedback with variable gains and time delays are considered here. Elimination of tonal vibration, real-time tunability, and stand-alone nature of these actively controlled absorbers are already proven features. The stability of the primary structure combined with multiple DR’s is addressed in this paper, following a stability chart strategy. A “peeling-off” procedure is adopted to eliminate successively the highest order delay terms in the characteristic equation of the system at each step. Consequently, the stability charts are constructed to reveal the operable zones. An example case of two identical DR’s on a 3-DOF system is presented.
The Effect of Spatially Nonuniform Thermal Fields on the Vibration Frequencies of EDM Wires
Authors: Murphy Kevin D. , Lin Zhengmao 
Published: January 2022

Abstract
This is an investigation into the effect of spatially nonuniform temperature fields on the undamped, free vibration characteristics of the wire electrode in the wire electro-discharge machining (EDM) process. In particular, a nonlinear multi-mode structural model is developed for the translating wire along with a thermal model which accounts for heat input (from sparking), axial conduction, radial convection, and energy storage. The two models are then coupled through the internal thermal stress terms of the structural model.
Using these combined models, an eigenvalue analysis is performed to examine the behavior of the natural frequencies (Im(λ)) as a function of the transport speed. It is shown that both divergence and Hopf bifurcations occur in this system. Specifically, the system is unstable at low transport speeds due to thermal buckling, stable at intermediate speeds, and unstable at high speeds due to a series of transport instabilities. Furthermore, it is shown that the frequency loci for a given mode decreases as the input discharge energy and, hence, the mean wire temperature are increased. This lowers the critical transport speed associated with the transport instability.
Laminar Natural Convection in Isosceles Triangular Enclosures Heated From Below and Symmetrically Cooled From Above
Authors: Holtzman Gary A. , Hill Roger W. , Ball Kenneth S. 
Published: January 2022

Abstract
A numerical study of natural convection in an isosceles triangular enclosure with a heated horizontal base and cooled upper walls is presented. Nearly every previous study conducted on this subject to date has assumed that the geometric plane of symmetry is also a plane of symmetry for the flow. This problem is re-examined over aspect ratios ranging from 0.2 to 1.0 and Grashof numbers from 103 to 105. It is found that a pitchfork bifurcation occurs at a critical Grashof number for each of the aspect ratios considered, above which the symmetric solutions are unstable to finite perturbations whereas two steady mirror image solutions are stable. Results are presented detailing the occurrence of the pitchfork bifurcation in each of the aspect ratios considered and the resulting flow patterns are described. Local and mean heat transfer coefficients are presented, and discrepancies with previously published results in which a symmetric flow pattern is assumed are discussed.
Heat Transfer to Two-Phase: Air, Power-Law Fluid Flows Over a Hot Cylinder
Authors: Rao B. K. 
Published: January 2022

Abstract
Circumferential temperatures for two-phase: air and aqueous polymer (purely viscous) solutions flowing over a horizontal cylinder were measured experimentally. The cylinder was heated by passing direct electric current through it. The peripherally averaged heat transfer coefficient for purely viscous non-Newtonian fluids, at any fixed flow rate, decreases with increasing polymer concentration. A new correlation is proposed for predicting the Nusselt number for two-phase: air and power-law fluid flows over a heated cylinder in cross flow.
Effect of Jet Characteristics on Heat Transfer by Impingement of Submerged-Confined Water Jet
Authors: Abou-Ziyan H. Z. , Radwan M. S. , Swidan M. M. , Ibrahim T. A. 
Published: January 2022

Abstract
Single phase forced convection and subcooled flow boiling due to impingement of confined submerged, fully turbulent liquid jet are experimentally investigated at atmospheric pressure. Heat transfer measurements are made along a uniformly heated surface onto which a jet is impinged orthogonal or at angles of inclination upstream into the cross flow. The experiments are performed at heat fluxes of 80–700 kW/m2, for cast iron and cast steel stabilized surfaces. The experimental parameters used in this investigation include: fluid temperatures (50, 60, 70 and 90°C), jet velocities (1, 2, and 3 m/sec), jet diameters (4.6, 8.6, and 10 mm), jet inclination angles (46°, 59°, and 90°), dimensionless nozzle-to-plate spacing distances, x/L (0.25, 0.5 and 1) with the duct heights, L of 10, 30 and 40 mm which provide confined walls aspect ratios (height/width) of 0.2, 0.6, and 0.8, respectively. Such conditions explore the effect of jet characteristics on cooling of engine cylinder heads by water impinging technique.
The results revealed that the heat flux is enhanced with degree of subcooling, flow velocity, jet diameter, jet inclination angle and confined wall aspect ratio. Correlations of forced convection, incipient boiling, partial subcooled flow boiling and fully developed subcooled boiling are obtained. These correlations are useful in designing the cooling system of the critical areas which cooled by jet impinging technique. The results showed that this technique can save 50% to 92% of the required cooling water when compared with the classical cooling technique.
Energy Dissipation in Sheared Granular Flows
Authors: Karion Anna , Hunt Melany L. 
Published: January 2022

Abstract
Flows of granular materials play an important role in industry and in nature. This research focuses on shear flows of particles of the same size and of two different sizes and the energy dissipation associated with these flows. The study was performed using a two dimensional discrete element computer simulation of a bounded, gravity-free Couette flow of particles. The heat dissipation rate per unit area in these flows is presented as a function of position in the flow as well as overall solid fraction. Results compare favorably with kinetic theory results from Jenkins and Richman (1985) for rough disks. The heat dissipation rate is also measured for binary mixtures of particles as a function of position in the flow and solid fraction ratio of small to large particles. These results are presented for diameter ratios of ten, five, and two. Results show that dissipation rates increase significantly with overall solid fraction and local strain rates and granular temperatures.