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RESEARCH PAPERS: Vibration and Sound

J. Vib., Acoust., Stress, and Reliab. 1986;108(4):389-393. doi:10.1115/1.3269360.

The in-plane and out-of-plane buckling of a beam subjected to axial loads due to steady rotation are investigated for various boundary conditions. The critical spin rate which will cause the beam to buckle is derived as a function of system parameters using Liapunov’s direct method. A significant advantage is offered by this method in that the equations of motion do not have to be solved in order to determine stability. Results are compared with those found in the literature.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):394-398. doi:10.1115/1.3269361.

The use of a Nyquist plot of the H2 (Syy /Sxy *) frequency response function estimates produced by an FFT based spectrum analyzer with random excitation to obtain modal amplitudes and hence modal constants has been investigated. It has been proved that, irrespective of the frequency resolution used, the H2 estimates always lie on the true modal circle so even at coarse frequency resolution, a circle fitted to these points gives accurate values of modal amplitude. The conventional H1 (Sxy /Sxx ) estimates lie inside the true modal circle. Use of the H2 technique results in major savings in the testing time required for a modal survey, particularly when measurements are to be taken at many points on the test structure.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):399-404. doi:10.1115/1.3269362.
Abstract
Topics: Density , Shells
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):405-410. doi:10.1115/1.3269363.

Kron’s method of dynamic substructure coupling is modified and extended to a form which is well suited for use with large finite-element substructure models. It is shown how both mass condensation and modal truncation can be applied at the substructure level in a manner compatible with the Kron coupling procedure. Either master or slave freedoms may be used as coupling coordinates in the system model, thereby allowing complete flexibility at the substructure analysis stage and in particular, allowing the use of automatic master selection procedures. Substructures may be coupled either directly or through a flexible interlayer. System damping may thus be represented in a fairly general way with each substructure having its own (uniform) damping level but with the further provision of additional damping at the joining surfaces between substructures. The theory is illustrated by examples with simple mass-spring systems.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):411-420. doi:10.1115/1.3269364.

A simple constructive technique for the development of rate-type hysteresis models for general nonlinear system is presented. The technique is used to develop hysteresis models to incorporate time history-dependent postyield restorting forces, and general pinching behavior in smoothly varying deteriorating models. Applications of these models to random vibration analysis modeling via simulation and equivalent linearization techniques under Gaussian noise excitation is presented.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):421-426. doi:10.1115/1.3269365.

The dynamic response of a two degree-of-freedom system with autoparametric coupling to a wide band random excitation is investigated. The analytical modeling includes quadratic nonlinearity, and a general first-order differential equation of the moments of any order is derived. It is found that the moment equations form an infinite hierarchy set which is closed via two different closure methods. These are the Gaussian closure and the non-Gaussian closure schemes. The Gaussian closure solution shows that the system does not reach a stationary response while the non-Gaussian closure solution gives a complete stationary steady-state response. In both cases, the response is obtained in the neighborhood of the autoparametric internal resonance condition for various system parameters.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):427-433. doi:10.1115/1.3269366.

Naturally limited stiffness of cantilever elements due to lack of constraint from other structural components, together with low structural damping, causes intensive and slow-decaying transient vibrations as well as low stability margins for self-excited vibrations. In cases of dimensional limitations (e.g., boring bars), such common antivibration means as dynamic vibration absorbers have limited effectiveness due to low mass ratios. This paper describes novel concepts of structural optimization of cantilever components by using combinations of rigid and light materials for their design. Two examples are given: tool holders (boring bars) and robot arms. Optimized boring bars demonstrate substantially increased natural frequencies, together with the possibility of greatly enhanced mass ratios for dynamic vibration absorbers. Machining tests with combination boring bars have been performed in comparison with conventional boring bars showing superior performance of the former. Computer optimization of combination-type robot arms has shown a potential of 10–60 percent reduction in tip-of-arm deflection, together with a commensurate reduction of driving torque for a given acceleration, and a higher natural frequencies (i.e., shorter transients). Optimization has been performed for various ratios of bending and joint compliance and various payloads.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):434-440. doi:10.1115/1.3269367.

In this paper, the equivalent linearization of an intershaft squeeze film damper in a two shaft engine system is investigated. The two shaft centers at the damper position are assumed to move in different elliptical offset orbits and at synchronous frequency with the unbalanced rotor (e.g., the high pressure rotor). The nonlinear damper force is resolved into two orthogonal components along the absolute coordinate directions and, in turn, each of these force components is supposed to be equivalent to the sum of an average force, a linear spring force, and a linear damping force in the corresponding direction. By using the method of equivalent linearization by harmonic balance, the six parameters of the equivalent forces, including two average forces, two equivalent spring coefficients, and two equivalent damping coefficients, are expressed analytically by the squeeze film forces and the assumed orbital motion of the two shaft centers at the damper position. The analytical expressions of the squeeze film forces are derived from an approximate solution of the basic Reynolds equation. The results obtained are verified by the method of equivalent linearization by minimum mean square errors. It shows that the six obtained parameters make the mean square errors minimum over a cycle period of motion, the errors being the difference between the equivalent forces and the actual nonlinear forces.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):441-446. doi:10.1115/1.3269368.

Results of an investigation on wave propagation in two-dimensional fluid-filled piping systems is reported. This phenomenon is studied by first developing a model for the transmission of solid-borne and fluid-borne vibrations in fluid-filled piping system elements, such as bends and straight sections. The aforementioned model, which is represented by an element transmission matrix, is used to determine the transfer and point impedances between the motion and forces of both the pipe and the fluid at any point within the element. It allows for longitudinal vibrations in the fluid, and longitudinal and bending vibrations in the solid portion of the system. The effects of both shear strains and rotary inertia within the pipe are included, while the effects of fluid flow and radial or angular modes in the fluid are neglected. Computer results for two-dimensional piping systems with modes of vibration in the plane of the pipes are considered. This method which is exact, except for possible computational errors, can be easily extended to the three-dimensional case.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Noise Control and Acoustics

J. Vib., Acoust., Stress, and Reliab. 1986;108(4):447-453. doi:10.1115/1.3269369.

The solution of an isoparametric, overdetermined formulation of the Helmholtz Integral is presented and demonstrated in three examples of acoustic radiation from spherical sources. The placement of the interior, overdetermining points is discussed and guidelines concerning surface element size are developed and tested. The total radiated sound power and transient acoustic response of a dilating sphere are computed.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):454-461. doi:10.1115/1.3269370.

This paper describes the applications of the Boundary-Element Method (BEM) for studies on acoustical field of various vibrating structures. The studies emphasize the numerical aspects of the BEM. Both acoustical near and far fields of the vibrating structures are investigated in this work. The vibrating structures considered in this application studies are a circular piston in an infinite, rigid baffle and cantilever-type beams. In the case of piston in an infinite baffle, instead of using the method of images, the free-space Green’s function is used to evaluate boundary integral equation by including both piston and baffle surfaces. The influence of the stationary baffle in the case of piston is further investigated. The beams considered are of both rectangular and circular cross sections. The results obtained by BEM have compared well with the available results from classical methods. The studies indicate that in the application of BEM in such problems both the element size and the number of elements including stationary surface have significant effect on the results obtained. The studies have yielded that very good results are obtained when the largest dimension of an element is equal to 0.2 times the acoustic wavelength (in air) of the frequency of acoustic radiation.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Reliability, Stress Analysis, and Failure Prevention

J. Vib., Acoust., Stress, and Reliab. 1986;108(4):462-468. doi:10.1115/1.3269371.

Several parameters for evaluating the decrease in structural stiffness in nonlinear finite element problems are defined here. Two types of parameters were considered: those that measure the overall softening and those that measure only a selected type of response, such as ovalization or bending. These parameters were used for detecting the approach of limit points in cylinder buckling problems under combined bending and external pressure. This is necessary for determining when the Newton-Raphson scheme should be replaced by displacement control to prevent numerical instability. The two types of parameters used in conjunction provide not only a reliable means for sensing the approach of limit points but also a determination of buckling modes.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Design Education

J. Vib., Acoust., Stress, and Reliab. 1986;108(4):469-473. doi:10.1115/1.3269372.

Corrosion-assisted cracking is treated as a time-dependent failure mechanism and is contrasted with other time-dependent phenomena, most notably fatigue. Two cases of failure are reviewed as examples of corrosion-assisted cracking. One case involves a surgical instrument which failed during an operation; the other involves a woman’s shoe. Both cases are documented with electron photomicrographs of the fractured surfaces. Basic features of corrosion-assisted cracking are reviewed and reference literature is cited.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Vib., Acoust., Stress, and Reliab. 1986;108(4):474-475. doi:10.1115/1.3269373.
Abstract
Topics: Vibration
Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Vib., Acoust., Stress, and Reliab. 1986;108(4):477-479. doi:10.1115/1.3269376.
FREE TO VIEW
Abstract
Topics: Noise (Sound)
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):479-480. doi:10.1115/1.3269377.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):480-482. doi:10.1115/1.3269378.
FREE TO VIEW
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):482-483. doi:10.1115/1.3269379.
FREE TO VIEW
Abstract
Topics: Vibration
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):483-484. doi:10.1115/1.3269380.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(4):484-485. doi:10.1115/1.3269381.
FREE TO VIEW
Abstract
Topics: Safety , Reliability
Commentary by Dr. Valentin Fuster

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