The Effect of Viscosity on the Forced Vibrations of a Fluid-Filled Elastic Shell

1983 ◽  
Vol 50 (3) ◽  
pp. 517-524 ◽  
Author(s):  
T. C. Su
Keyword(s):  
Essential Feature ◽  
Elastic Shell ◽  
Energy Dissipation Rate ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
External Forcing ◽  
Fluid Loading ◽  
Response Curves ◽  
Frequency Spectra ◽  
Resonant Frequencies

The effect of viscosity on the axisymmetric, forced vibrations of a fluid-filled, elastic, spherical shell is studied analytically. Necessary theory, using boundary layer approximation for the fluid as developed in a previous paper for free vibrations, has been extended to incorporate an external forcing excitation. Shell response, fluid loading, and energy dissipation rate are computed for radial, tangential, and combined force excitations. The essential feature of the modal and the total responses is determined by resonant frequencies and various vibration-absorbing frequencies. Frequency spectra for such frequencies, as well as various response curves, are presented in dimensionless forms to illustrate the characteristics of the solution.

scholarly journals Compensatory bellows oscillations as a corrugated shell with liquid inside

2021 ◽  
pp. 31-40
Author(s):  
T. V Zinovieva ◽  
V. A Piskunov
Keyword(s):  
Degrees Of Freedom ◽  
Natural Frequencies ◽  
Elastic Shell ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
Compressible Liquid ◽  
Plastic State ◽  
Material Surface ◽  
Attached Mass ◽  
Corrugated Shell

The paper deals with a relevant problem of shipbuilding, i.e. calculation of free and forced vibrations of pipeline compensatory bellows. These devices are used to reduce the vibration load caused by ship power machines. When analyzing the vibrations of the compensatory bellows, it is necessary to take into account the liquid contained in the bellows. In this work, the design model of the bellows is represented by a corrugated elastic shell as a material surface with five degrees of freedom. A variant of the classical theory of shells, built on the basis of Lagrangian mechanics, is used. The influence of the liquid is taken into account by two models. First, the liquid is considered to be ideal and incompressible and is considered through the attached mass to the shell. The shell is replaced by a cylindrical surface with a radius in the middle line of the corrugation. To account for the influence of the frequency of bellows oscillations on the attached inertia of the liquid in the calculation we also used the acoustic approximation; and derived a formula for a generalized attached mass of the ideal compressible liquid. The equations of the bellows oscillations under the periodic loading are obtained. The problem has been solved by the finite difference method. The values of natural frequencies of free vibrations are obtained for the compensatory bellows from the corrosion-resistant heat-resistant steel. It is shown that by taking account of the liquid, we significantly change the natural frequencies of the bellows. With high-frequency vibrations it is necessary to take into account the compressibility of the liquid. The problem of the forced vibrations of the bellows caused by a displacement of its end face by the harmonic law is solved. The internal forces and moments are determined, as well as occurring stresses by Mises criterion in the bellows. We found the critical value of the end face displacement at a frequency of 50 Hz, at which the bellows goes into a plastic state.

Vibration of an Infinitely Extending Plate Resting on an Elastic Foundation

1963 ◽  
Vol 30 (3) ◽  
pp. 355-362 ◽  
Author(s):  
Kazuyosi Ono
Keyword(s):  
Free Vibration ◽  
Elastic Foundation ◽  
Infinite Number ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
The Other ◽  
Damped Oscillation

Free vibrations and forced vibrations of an infinitely extending plate resting on an elastic foundation and carrying a mass are solved. Then the amplitudes of the free vibrations produced by an impulse applied to the mass on the plate are determined, and it is found that two kinds of vibration are produced in the plate: One is a free vibration and the other is a special vibration, which consists of an infinite number of free vibrations and resembles a damped oscillation.

Vibrations of Double-Walled Carbon Nanotubes With Different Boundary Conditions Between Inner and Outer Tubes

2008 ◽  
Vol 75 (2) ◽  
Author(s):  
Kai-Yu Xu ◽  
Elias C. Aifantis ◽  
Yong-Hua Yan
Keyword(s):  
Carbon Nanotubes ◽  
Boundary Conditions ◽  
Resonant Frequency ◽  
Free Vibrations ◽  
Original Method ◽  
Reduced Form ◽  
Vibrational Modes ◽  
Resonant Frequencies ◽  
Different Boundary Conditions ◽  
Double Walled Carbon Nanotubes

Free vibrations of a double-walled carbon nanotube (DWNT) are studied. The inner and outer carbon nanotubes are modeled as two individual elastic beams interacting each other by van der Waals forces. An original method is proposed to calculate the first seven order resonant frequencies and relative vibrational modes. Detailed results are demonstrated for DWNTs according to the different boundary conditions between inner and outer tubes, such as fixed-free, cantilever-free, fixed-simple and fixed-fixed (reduced form) supported ends. Our results indicate that there is a special invariable frequency for a DWNT that is not affected by different combinations of boundary conditions. All vibrational modes of the DWNT must be coaxial when the resonant frequency is smaller than this frequency. Some noncoaxial vibrations will occur when their resonant frequencies exceed the frequency. Especially, the first noncoaxial resonant frequency is still invariable for all different boundary conditions. A change of resonant frequency for various lengths of DWNTs is discussed in detail. In addition, our model predicts a new coaxial-noncoaxial vibrational mode in fixed-simple supports for inner and outer tubes of a DWNT.

Detection of Cracks in Rotating Timoshenko Shafts Using Axial Impulses

1991 ◽  
Vol 113 (1) ◽  
pp. 74-78 ◽  
Author(s):  
K. R. Collins ◽  
R. H. Plaut ◽  
J. Wauer
Keyword(s):  
Piecewise Linear ◽  
Equations Of Motion ◽  
Crack Depth ◽  
Effective Means ◽  
Linear Equations ◽  
Free Vibrations ◽  
Frequency Spectra ◽  
Time Histories ◽  
Rotating Shafts ◽  
Linear Equations Of Motion

A rotating Timoshenko shaft with a single transverse crack is considered. The crack opens and closes during motion and is represented by generalized forces and moments. The shaft has simply supported ends, and the six coupled, piecewise-linear equations of motion (including longitudinal, transverse, and torsional displacements) are integrated numerically after application of Galerkin’s method with two-term approximations for each of the six displacements. Time histories and frequency spectra are compared for shafts with no crack and with a crack for which the crack depth is one-fifth of the shaft diameter. Free vibrations and the responses to a single axial impulse and periodic axial impulses are analyzed. The last case appears to provide an effective means for detecting cracks in rotating shafts.

An Asymptotic Method to Analyze the Vibrations of an Elastic Layer

1969 ◽  
Vol 36 (1) ◽  
pp. 65-72 ◽  
Author(s):  
J. D. Achenbach
Keyword(s):  
Power Series ◽  
Boundary Conditions ◽  
Equations Of Motion ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
Wave Number ◽  
Dimensionless Wave Number ◽  
Analogous Manner ◽  
Independent Variable ◽  
Thickness Variable

The displacement components for both free and forced vibrations are sought as power series of the dimensionless wave number ε, where ε = 2π × layer thickness/wavelength. For the free vibration problem the object is to determine the frequencies, which are also sought as power series of the dimensionless wave number. The displacement and frequency expansions are substituted in the displacement equations of motion and in the boundary conditions. By collecting terms of the same order εn, a system of second-order, inhomogeneous, ordinary differential equations of the Helmholtz type is obtained, with the thickness variable as independent variable, and with associated boundary conditions. For free vibrations, subsequent integration yields the coefficients of εn for the displacements and the frequencies for all modes, and in the whole range of frequencies, but in a range of dimensionless wave numbers 0 < ε < ε* < 1, where ε* increases as more terms are retained in the expansions. For forced vibrations, the amplitudes are determined in an analogous manner if the external surface tractions are of sinusoidal dependence on the in-plane coordinates and on time. The response to surface tractions of more general spatial dependence is obtained by Fourier superposition.

Axisymmetric Vibrations of a Piezoelectric Spherical Shell Submerged in a Compressible Viscous Fluid Medium

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Juxi Hu ◽  
Zhiping Qiu ◽  
Tsung-Chow Su
Keyword(s):  
Viscous Fluid ◽  
Natural Frequencies ◽  
Essential Feature ◽  
Elastic Shell ◽  
Dynamic Responses ◽  
Mode Shapes ◽  
Compressible Viscous Fluid ◽  
Previous Theory ◽  
Fluid Medium ◽  
Shell Motion

Axisymmetric vibrations of a hollow piezoelectric sphere submerged in a compressible viscous fluid medium are investigated. The piezoelectric sphere is radially polarized. The differential equations governing the shell motion are obtained by the use of Hamilton’s principle. Based on the classical bending theory of shells, it is shown that all the piezoelectric contributions can be included in the in vacuo natural frequencies and their corresponding mode shapes. As such, the previous theory on elastic shell vibration becomes readily extendable. The flow field, determined by the boundary layer theory, is coupled to the shell motion through no-slip and no-penetrating conditions. It is found that the contribution of the piezoelectric parameters in the thin shell’s free vibration is of small order and is negligible. Natural frequencies and their associated vibration characteristics are numerically obtained and presented for a Polyvinglindene fluoride (PVDF) shell submerged in water. Dynamic responses of a submerged piezoelectric sherical shell, and the associated radiation of sound are investigated. The oscillations are harmonically driven by an axisymmetrically applied electric potential difference across the surface of the shell. The vibrational, fluid loading, and energy flow characteristics are derived and evaluated for a PVDF shell submerged in water. The essential feature of the modal response is determined by various critical frequencies, such as resonant frequencies and vibration-absorbing frequencies. Viscous effect is found noticeable in several cases.

Forced Vibrations of Viscoelastic Timoshenko Beams

1976 ◽  
Vol 98 (3) ◽  
pp. 820-826 ◽  
Author(s):  
C. C. Huang ◽  
T. C. Huang
Keyword(s):  
Boundary Conditions ◽  
Laplace Transform ◽  
Attenuation Factor ◽  
Equations Of Motion ◽  
Bending Moment ◽  
Expansion Method ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
Mode Shapes ◽  
Timoshenko Beams

In a previous paper, the correspondence principle has been applied to derive the differential equations of motion of viscoelastic Timoshenko beams with or without external viscous damping. To study free vibrations these equations are solved by Laplace transform and boundary conditions are applied to obtain the attenuation factor and the frequency of the damped free vibrations and mode shapes. The present paper continues to analyze this subject and deals with the responses in deflection, bending slope, bending moment and shear for forced vibrations. Laplace transform and appropriate boundary conditions have been applied. Examples are given and results are plotted. The solution of forced vibrations of elastic Timoshenko beams obtained as a result of reduction from viscoelastic case and by eigenfunction expansion method concludes the paper.

Response Bounds for Linear Damped Systems

1999 ◽  
Vol 66 (4) ◽  
pp. 997-1003 ◽  
Author(s):  
B. Hu ◽  
P. Eberhard
Keyword(s):  
State Vector ◽  
Displacement Vector ◽  
Harmonic Excitation ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
The State ◽  
Euclidean Norm ◽  
Damped Systems

In this paper response bounds of linear damped systems are reviewed and new response bounds are presented for free vibrations and forced vibrations under impulsive, step, and harmonic excitation. In comparison to the response bounds available in the literature, the ones presented here are not only closer to the exact responses, but are also simpler to compute. Previous bounds are given only on the Euclidean norm of the state vector or the displacement vector. Here, the response bounds are also given on individual coordinates, information which is more meaningful in engineering.

scholarly journals Estimation of Turbulence Parameters in the Lower Troposphere from ShUREX (2016–2017) UAV Data

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 384 ◽  
Author(s):  
Hubert Luce ◽  
Lakshmi Kantha ◽  
Hiroyuki Hashiguchi ◽  
Dale Lawrence
Keyword(s):  
Richardson Number ◽  
Layer Structure ◽  
Lower Troposphere ◽  
Energy Dissipation Rate ◽  
Function Parameter ◽  
Mixing Efficiency ◽  
Temperature Structure ◽  
Frequency Spectra ◽  
Kolmogorov Turbulence ◽  
Turbulence Parameters

Turbulence parameters in the lower troposphere (up to ~4.5 km) are estimated from measurements of high-resolution and fast-response cold-wire temperature and Pitot tube velocity from sensors onboard DataHawk Unmanned Aerial Vehicles (UAVs) operated at the Shigaraki Middle and Upper atmosphere (MU) Observatory during two ShUREX (Shigaraki UAV Radar Experiment) campaigns in 2016 and 2017. The practical processing methods used for estimating turbulence kinetic energy dissipation rate ε and temperature structure function parameter C T 2 from one-dimensional wind and temperature frequency spectra are first described in detail. Both are based on the identification of inertial (−5/3) subranges in respective spectra. Using a formulation relating ε and C T 2 valid for Kolmogorov turbulence in steady state, the flux Richardson number R f and the mixing efficiency χ m are then estimated. The statistical analysis confirms the variability of R f and χ m around ~ 0.13 − 0.14 and ~ 0.16 − 0.17 , respectively, values close to the canonical values found from some earlier experimental and theoretical studies of both the atmosphere and the oceans. The relevance of the interpretation of the inertial subranges in terms of Kolmogorov turbulence is confirmed by assessing the consistency of additional parameters, the Ozmidov length scale L O , the buoyancy Reynolds number R e b , and the gradient Richardson number Ri. Finally, a case study is presented showing altitude differences between the peaks of N 2 , C T 2 and ε , suggesting turbulent stirring at the margin of a stable temperature gradient sheet. The possible contribution of this sheet and layer structure on clear air radar backscattering mechanisms is examined.

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