Showing papers in "Journal of Sound and Vibration in 1978"
TL;DR: In this article, three different approaches to the subject are identified, consisting of theories based on Lighthill's acoustic analogy, the solution of special, linearized hydroacoustic problems, and ad hoc aerodynamic source models.
Abstract: Literature on the theory of the generation of sound by the interaction of low Mach number turbulent flow with the edge of a semi-infinite rigid plate is critically reviewed. Three different approaches to the subject are identified, consisting of theories based on (1) Lighthill's acoustic analogy; (2) the solution of special, linearized hydroacoustic problems; and (3) ad hoc aerodynamic source models. When appropriately interpreted, all relevant theories produce essentially identical predictions in the limit of very small Mach numbers. None of the theories discusses the implications of the Kutta condition, however, nor of the effect of forward flight and source motion relative to the trailing edge. An outline of a redevelopment of the theory is included to give a unified view of the problem, exhibit the significance of the various approximations, and incorporate the effect of mean motion and of the Kutta condition.
520 citations
TL;DR: In this article, a comparison between several shear layer refraction theories is made to determine their relationship to one another and to determine which parameters are important for an open jet wind tunnel shear-layer correction.
Abstract: A comparison is made between several shear layer refraction theories to determine their relationship to one another and to determine which parameters are important for an open jet wind tunnel shear layer correction. For sound transmission through a parallel sheared flow, the shear layer thickness is found to be unimportant at Mach numbers typical of open jet tunnels. The effect of reflected waves, although more significant, can usually be ignored, allowing a correction which is independent of source type and frequency. The shear layer shape (plane or cylindrical) can be important and the correction corresponding to the actual shear layer shape should be used. The numerical solutions of the Lilley equation for the limiting cases of a thick and a thin shear layer are found to agree with the algebraic expressions given for these limiting cases.
312 citations
TL;DR: In this paper, a linear dynamic analysis of bridge flutter for bridges having vibration modes that are not necessarily simple, i.e., that may involve motions beyond pure flexure and torsion, is presented.
Abstract: The action of long-span bridges, notably suspension bridges, under wind has long been of concern. This first of two papers summarizes the pertinent experimental and other prerequisite data and proceeds to the linear dynamic analysis of bridge flutter for bridges having vibration modes that are not necessarily simple, i.e., that may involve motions beyond pure flexure and torsion. A review is made of the energy considerations involved in the assessment of aerodynamic stability. The paper lays the groundwork for the one that follows.
288 citations
TL;DR: In this paper, the problem of bridge buffeting under natural wind is considered, and the buffeting action of random wind forces in the presence of self-excited, or bridge motion-induced, forces is discussed, as well as energy considerations associated with bridge stability.
Abstract: By using the analytical and conceptual format set forth in the first of these two companion papers, the problem of bridge buffeting under natural wind is considered. Again, bridges having vibration modes that are not necessarily simple are dealth with. The buffeting action of random wind forces in the presence of self-excited, or bridge motion-induced, forces is discussed, as are energy considerations associated with bridge stability. A possible explanation is offered for the well-known fact that turbulence in the incident wind often delays the onset of flutter.
225 citations
TL;DR: The most fundamental cause of noise and unsteady running of rolling bearings is the so-called varying compliance vibrations that occur irrespective of the quality and accuracy of the bearing.
Abstract: The most fundamental cause of noise and unsteady running of rolling bearings is the so-called varying compliance vibrations. These are parametrically excited vibrations that occur irrespective of the quality and accuracy of the bearing. Varying compliance of the bearing assembly can give rise to both radial and axial displacements of a shaft supported by rolling bearings. In this study, however, attention is focused on radial vibrations of radially loaded bearings having a positive radial clearance. Previous studies of this phenomena are quasi-static in approach—the inclusion of inertia forces reveals characteristics not previously recognized. Examples of theoretical solutions obtained through digital simulation are presented and comparisons with experimentally obtained results are made.
208 citations
TL;DR: In this article, the authors developed a procedure for generating the sound fields radiated by arbitrarily shaped, three dimensional bodies from an integral representation of the solutions of the Helmholtz equation.
Abstract: This paper is concerned with the development of a procedure for generating the sound fields radiated by arbitrarily shaped, three dimensional bodies from an integral representation of the solutions of the Helmholtz equation The method of Burton and Miller is employed to eliminate the non-uniqueness in the external Helmholtz formulae which occurs at the internal eigenfrequencies of the geometry under consideration Also, a representation of the most singular component in the Burton and Miller formulation is developed resulting in an integral equation which is amenable to numerical solutions A simple numerical scheme is introduced which reduces the large amounts of computer storage and time normally required for the solution of similar problems This numerical scheme is then used to obtain solutions for the radiated sound field generated by a vibrating piston set in a sphere The numerical solutions for the surface and far field sound patterns are compared with exact analytical solutions and deviations of 10% at most are noted Since the symmetry of the sphere was not taken advantage of in these computations, the numerical schemes employed are applicable to general three dimensional sound radiation problems
197 citations
TL;DR: In this paper, a review of the effects of low frequency noise indicates that the effects are similar to those of higher frequency noise, that noise in the 20-100 Hz range is much more significant than infrasound at similar sound pressure levels and that the possible danger due to Infrasound has been much over-rated.
Abstract: During the fast few years, the existence of high levels of man-made low frequency noise (0–100 Hz), and in particular infrasonic noise, has been reported in many environments. An effort has been made over the last decade to discover whether such high levels of low frequency noise are significant. A review of the effects of low frequency noise indicates that the effects are similar to those of higher frequency noise, that noise in the 20–100 Hz range is much more significant than infrasound at similar sound pressure levels and that the possible danger due to infrasound has been much over-rated.
147 citations
TL;DR: In this article, the authors determined the lead-lag natural frequencies and mode shapes of a radial beam mounted on a rotating disc at a 90° setting angle by means of the finite element technique, a high precision beam element based on a fifth degree polynomial being used as displacement function, with deflection and slope at the ends as common nodal degrees of freedom.
Abstract: Lead-lag natural frequencies and mode shapes of a radial beam mounted on a rotating disc at a 90° setting angle are determined. The solution was obtained by means of the finite element technique, a high precision beam element based on a fifth degree polynomial being used as displacement function, with deflection and slope at the ends as common nodal degrees of freedom, and two integrals over the element length as nodeless additional degrees of freedom. Effects such as shearing force, rotary inertia and varying centrifugal forces are taken into consideration. Results found in the literature for a cantilever beam are in good agreement with present results. The case of a beam blade with shroud mass is also considered.
142 citations
130 citations
TL;DR: In this paper, a technique is developed to give the optimal dynamic vibration absorber parameters for the elimination of excessive vibration in sinusoidally forced Bernoulli-Euler beams.
Abstract: A technique is developed to give the optimal dynamic vibration absorber parameters for the elimination of excessive vibration in sinusoidally forced Bernoulli-Euler beams. The result is presented in a general form so as to include all possible sets of ordinary boundary conditions and absorber attachment points. This is done by employing a single mode expansion for the beam in an assumed mode approach. The general equations developed are then applied to a point-forced cantilever beam with a viscously damped dynamic absorber attached at the beam midpoint. The optimal values developed for the single mode approximation are then evaluated with account taken of the first five beam modes where discrepancies are noted near the higher order beam resonances which are shifted somewhat due to the absorber.
117 citations
TL;DR: In this article, a new approach to the free vibration analysis of the completely free rectangular plate has been proposed, by using the method of superposition, and it is shown that solutions which satisfy identically the differential equation and which satisfy the boundary conditions with any desired degree of accuracy are obtained.
Abstract: While the subject of free vibration analysis of the completely free rectangular plate has a history which goes back nearly two centuries it remains a fact that most theoretical solutions to this classical problem are considered to be at best approximate in nature. This is because of the difficulties which have been encountered in trying to obtain solutions which satisfy the free edge conditions as well as the governing differential equation. In a new approach to this problem, by using the method of superposition, it is shown that solutions which satisfy identically the differential equation and which satisfy the boundary conditions with any desired degree of accuracy are obtained. Eigenvalues of four digit accuracy are provided for a wide range of plate aspect ratios and modal shapes. Exact delineation is made between the three families of modes which are characteristic of this plate vibration problem. Accurate modal shapes are provided for the response of completely free square plates.
TL;DR: In this paper, the effect of the ratio c d, which is the ratio of the lengths of the sides of the rectangle, to the aeroelastic instability phenomena in the vicinity of the resonance speed was investigated.
Abstract: This paper deals with wind tunnel experiments on the aeroelastic instability in a heaving mode of two-dimensional rectangular cylinders in a uniform two-dimensional flow. Both the free oscillation method and the forced oscillation method are employed for the experiments. Emphasis is placed on finding the effect of the ratio c d , which is the ratio of the lengths of the sides of the rectangle, to the aeroelastic instability phenomena in the vicinity of the resonance speed. Emphasis is also placed on finding possible limitations in the application of the quasi-steady aerodynamic theory to the analysis of the aeroelastic characteristics.
TL;DR: In this paper, a simple approximate formula for the natural frequencies of flexural vibration of isotropic plates, originally developed by Warburton using characteristic beam functions in Rayleigh's method, is modified to apply to specially orthotropic plates and extended to include the effect of uniform, direct inplane forces.
Abstract: A simple approximate formula for the natural frequencies of flexural vibration of isotropic plates, originally developed by Warburton using characteristic beam functions in Rayleigh's method, is modified to apply to specially orthotropic plates and extended to include the effect of uniform, direct inplane forces. The initial buckling problem is treated simply by equating the frequency expression to zero. The approach permits the ready determination of reasonably accurate natural frequencies and/or buckling loads for a given plate involving any combination of free, simply supported or clamped edges, without requiring the aid of a sophisticated calculating device or a knowledge of plate, vibration or buckling theory. To illustrate the applicability and accuracy of the approach, numerical results for a number of specific plate problems are presented.
TL;DR: In this article, a low-tip speed axial flow fan with eight equally spaced blades was tested in both free field and reverberant field environments and the fan backpressure and speed were varied during the tests.
Abstract: Noise and performance tests were conducted on a low tip speed, half-stage, axial flow fan such as is used in automotive applications. The purpose of the tests was to determine the characteristics, relative importance, and the methods of control of the tip clearance noise of the fan. The fan was 356 mm in diameter and had eight equally spaced blades. The noise measurements were made in both free field and reverberant field environments and the fan backpressure and speed were varied during the tests. An acenaphthene coating on the blades was used to determine the regions of laminar and turbulent flow and smoke was used to visualize the blade-tip flow patterns. Tip clearance noise was shown to contribute up to 15 dB in overall noise level over the entire fan operating range for tip clearances of the order of 3–4% of the blade chord and larger. Large clearances result in a significant (∼10%) drop in fan peak efficiency. Essentially, tip clearance noise is due to interactions of the blade tip vortex with the trailing edge of the blade and with the leading edge of the following blade. A properly contoured, rotating ring-shroud attached to the fan tips was found to be a practical method of controlling tip clearance noise. For example, with a clearance of 6·5% of the chord length, the noise level with the ring-shroud was as much as 12 dB lower than in the fixed shroud case with the same clearance.
TL;DR: In this paper, the effects on the fluid elastic threshold of the motion of surrounding tubes, damping and number of upstream rows of tubes are discussed, as well as the turbulent buffeting and fluid elastic response are treated.
Abstract: Experimental results are reported for a wind tunnel study of cross-flow induced vibrations in a tube bank. The rotated triangular array had a pitch ratio of 1·375 and consisted of 19 flexibly mounted tubes surrounded by 116 rigid, removable tubes. The natural frequency and damping of the flexibly mounted tubes could be carefully controlled. Details of the experimental facility and the vortex shedding behaviour of the tube bank were reported in the first of these two companion papers. The turbulent buffeting and fluid elastic response are treated in this second paper. The effects on the fluid elastic threshold of the motion of surrounding tubes, damping and number of upstream rows of tubes are discussed.
TL;DR: In this article, the stiffness and mass matrices of a twisted beam element with linearly varying breadth and depth are derived, where the angle of twist is assumed to vary linearly along the length of the beam.
Abstract: The stiffness and mass matrices of a twisted beam element with linearly varying breadth and depth are derived. The angle of twist is assumed to vary linearly along the length of the beam. The effects of shear deformation and rotary inertia are considered in deriving the elemental matrices. The first four natural frequencies and mode shapes are calculated for cantilever beams of various depth and breadth taper ratios at different angles of twist. The results are compared with those available in the literature.
TL;DR: In this article, four finite strip models are developed for the flexural vibration analysis of rectangular plates based on Mindlin theory which takes account of transverse shear deformation and of rotary inertia.
Abstract: Four finite strip models are developed for the flexural vibration analysis of rectangular plates based on Mindlin theory which takes account of transverse shear deformation and of rotary inertia. The strips are simply supported at their ends and differ one from another in the order of interpolation employed to represent the variation of each of the plate deflection and the two rotations across the strip. The four models are based in turn on quadratic, cubic, quartic and quintic interpolation. Numerical results are presented of applications of the strip models to the calculation of the natural frequencies of both thin and moderately thick plates. The influence that the assumed value of the shear coefficient has on natural frequencies is considered for two particular moderately thick plates.
TL;DR: In this article, statistical error analysis formulas are developed for evaluating ordinary, partial and multiple coherence function estimates, and associated quantities which occur in analysis of single input/output problems and in multiple input-output problems, including estimates of coherent output spectra and estimates of gain and phase factors of related frequency response functions.
Abstract: Practical statistical error analysis formulas are developed for evaluating ordinary, partial and multiple coherence function estimates, and associated quantities which occur in analysis of single input/output problems and in multiple input/output problems. These include estimates of coherent output spectra and estimates of gain and phase factors of related frequency response functions. Models are either single input/output models or conditioned input/output models, where the latter models can be created from arbitrary measured multiple input/output data. Guidelines are presented to reduce statistical errors in such computed quantities. These results are essential for applications to identify different multiple noise sources, to determine multiple system properties, to measure response effects due to the sources acting singly or in various combinations, to simulate multiple random environments, and to predict system failures from response measurements only.
TL;DR: In this paper, an eight node isoparametric finite element is used to represent a rigid porous absorbing material and tests on an assembly of these elements for a one dimensional model gave good agreement with an exact solution for the input impedance.
Abstract: An eight node isoparametric finite element is used to represent a rigid porous absorbing material. Tests on an assembly of these elements for a one dimensional model gave good agreement with an exact solution for the input impedance. Results from a two dimensional model show the effects of transverse propagating modes on the input impedance and indicate that for an absorbent with finite dimensions extended reaction is important.
TL;DR: Experimental research into the effects on human vision of both object vibration and whole-body vibration is summarized and it is shown that while many factors are important and current understanding is far from complete, the literature does contain useful information.
Abstract: This is the first part of a review of the effects of vibration on vision and continuous manual control. In this part experimental research into the effects on human vision of both object vibration and whole-body vibration is summarized. Knowledge of the respective effects of vibration variables (principally amplitude, frequency and direction) and visual task variables (such as illumination, size and viewing distance) is discussed in separate sections. It is shown that while many factors are important and current understanding is far from complete, the literature does contain useful information. The conditions studied in those experiments concerned with the effects of whole-body vibration on vision are tabulated in the Appendix so as to provide a convenient guide to the literature.
TL;DR: In this paper, the authors proposed scaling laws for hot turbulent jet mixing noise outside the cone of silence to account for mean flow field effects on sound radiation via an analytical high frequency approximate solution to the Lilley's equation.
Abstract: New scaling laws are presented for hot turbulent jet mixing noise outside the cone of silence. These account for mean flow field effects on sound radiation via an analytical high frequency approximate solution to Lilley's equation. Numerical calculations for sound radiation from sources in a cylindrical shear flow are used to test the validity of the approximation. The proposed scaling laws yield an excellent collapse of jet noise measurements over a wide range of conditions. The resulting information has been incorporated into a jet mixing noise prediction scheme which, with appropriate modifications to the analytical high frequency approximation, can be applied both inside and outside the cone of silence. The prediction scheme for angles inside the cone of silence will be described in a subsequent paper.
TL;DR: In this article, a review of the effects of vibration on human performance is presented, with a focus on continuous manual control, or tracking, and the results of most of the laboratory studies of vibration and tracking performance are separately summarized in tabular form in the Appendix.
Abstract: This second, and final, part of a review of the effects of vibration on human performance is concerned with continuous manual control, or tracking. As in the first part, which dealt with the effects of vibration on vision, the task and vibration variables which have been shown to affect the sensitivity of a task to vibration are discussed separately. Other sections are concerned with the measurement of tracking performance in vibration environments, general conclusions about the nature and mechanisms of the effects of vibration on tracking and the application of these conclusions in the form of predictive models. The procedures and results of most of the laboratory studies of vibration and tracking performance are separately summarized in tabular form in the Appendix as a convenient guide to the relevant literature.
TL;DR: In this article, a finite element method was developed for the study of transmission of sound in non-uniform ducts without flow, and the formulation is based on a weighted residual approach and eight noded isoparametric elements are used.
Abstract: A finite element method is developed for the study of transmission of sound in non-uniform ducts without flow. The formulation is based on a weighted residual approach and eight noded isoparametric elements are used. Two computational schemes are described, one based on the Helmholtz equation obtained by combining the basic conservation equations and one based on the conservation equations themselves. The latter case is considered because in future extensions to problems involving mean flow a single governing equation is not readily obtainable except for irrotational flows. Both two-dimensional and circular duct geometries are considered. Comparisons are made with a Method of Weighted Residuals in the form of a Modified Galerkin Method in the two-dimensional case to assess both accuracy and computational efficiency. It is found that the finite element method produces results for transmission and reflection coefficients nearly identical to those from the Galerkin approach. Used to its best advantage the finite element method is of comparable efficiency.
TL;DR: In this paper, the authors proposed a road surface model based on the assumption of isotropy and showed that a particular profile spectral density can be used to define an effective surface model, and validated the proposed model by comparison with coherencies based on measurement.
Abstract: Road surface description forms the basis of vehicle response prediction, but in most cases precise description of a particular road is of less value than a description representative of a class of roads. In these circumstances an analytical road surface model has special advantages. In modelling a road surface—rather than a single road profile—the hypothesis of isotropy is shown to provide a useful basis, and the paper shows how a particular profile spectral density, together with the assumption of isotropy, can be used to define an effective surface model. Coherence functions derived from the proposed model are validated by comparison with coherencies based on measurement.
TL;DR: In this article, a Timoshenko beam finite element is presented which has three nodes and two degrees of freedom per node, namely the values of the lateral deflection and the cross-sectional rotation.
Abstract: A Timoshenko beam finite element is presented which has three nodes and two degrees of freedom per node, namely the values of the lateral deflection and the cross-sectional rotation. The element properties are based on a coupled displacement field; the lateral deflection is interpolated as a quintic polynomial function and the cross-sectional rotation is linked to the deflection by specifying satisfaction of the governing differential equation of moment equilibrium in the absence of the rotary inertia term. Numerical results confirm that this procedure does not preclude convergence to true Timoshenko theory solutions since rotary inertia is included in lumped form at element ends. The new Timoshenko beam element has good convergence characteristics and where comparison can be made in numerical studies it is shown to be generally more efficient than previous elements.
TL;DR: In this paper, the dynamic stability of cylindrical shells under both static and periodic compressive forces is theoretically analyzed under four different boundary conditions, with the effect of the axisymmetric unperturbed bending vibration taken into consideration.
Abstract: Based on the Donnell equations modified with the transverse inertia force, the dynamic stability of circular cylindrical shells under both static and periodic compressive forces is theoretically analyzed under four different boundary conditions, with the effect of the axisymmetric unperturbed bending vibration taken into consideration. The problem is first reduced to that of a finite degree-of-freedom system with the Galerkin procedure, the stability of which is examined by using Hsu's method. Calculations are carried out for typical cases and the instability regions of the principal, secondary and combination parametric resonances are determined for the frequency range covering up to several times the lowest natural frequency. It is found, among others, that the effect of the unperturbed motion is quite significant for shells with moderate length while that of the longitudinal resonance is generally negligible for thin shells.
TL;DR: In this article, it was shown experimentally that the presence of tubes in a heat exchanger reduces the effective speed of sound in planes normal to the axes of the tubes, and the effective speeds were used to analyse the possible resonant acoustic modes of a rectangular duct containing a tube bank filling a section in the center of the duct.
Abstract: It is shown experimentally that the presence of the tubes in a heat exchanger reduces the effective speed of sound in planes normal to the axes of the tubes. The effective speeds are used to analyse the possible resonant acoustic modes of a rectangular duct containing a tube bank filling a section in the centre of the duct. Experimental results confirm the modes and the predicted frequencies.
TL;DR: In this article, the authors evaluated the differences in discomfort and body transmissibility between and within different population groups and attempted to discover physical causes of the differences and the significance of the findings to future research and the application of human response to vibration data.
Abstract: The experiment described in this paper was designed to evaluate the differences in discomfort and body transmissibility between and within different population groups and to attempt to discover physical causes of the differences. The responses of one hundred-and-twelve seated subjects to vertical (z-axis) sinusoidal vibration at 4 Hz and 16 Hz were investigated. The subjects were in three groups (56 men, 28 women and 28 children) and were of varied demography. In the first part of the experiment they were required to make seven judgments indicating which of seven levels (in the range 0·41 to 2·46 m/s 2 rms) of 16 Hz vibration caused more discomfort than a fixed level (1·0 m/s 2 rms) of 4 Hz vibration. In the second part of the experiment the transmission of vertical vibration from seat to head was measured at the same two frequencies. The large differences found between the responses of individual subjects are presented as frequency distributions. The subjective responses from each of the three populations were well approximated by log-normal distributions. Overall, the data indicate that, for the median subject, similar levels of the 4 Hz and 16 Hz vibration produced similar degrees of discomfort. However, within each population about 10% considered equivalence between the two motions occurred at a 16 Hz level more than double the median equivalent level and 10% considered equivalence occurred at less than about half the median equivalent level. For each subject group and at both frequencies the distributions of transmissibilities were approximately normal. Within groups there were significant correlations between transmissibility and subject size and between transmissibility and subjective response. The significance of the findings to future research and the application of human response to vibration data is discussed.
TL;DR: A system has been developed and tested for the balancing of rotating systems without interrupting operation and several procedures are proposed for balancing, in which only measurements of the bearing vibrations are used.
Abstract: A system has been developed and tested for the balancing of rotating systems without interrupting operation. Several procedures are proposed for balancing, in which only measurements of the bearing vibrations are used. Large generators, turbines, fans, pumps and compressors are potential applications.