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RESEARCH PAPERS: Vibration and Sound

J. Vib., Acoust., Stress, and Reliab. 1987;109(3):227-234. doi:10.1115/1.3269425.

In this report, through experiments the influence of five major geometric parameters on noise and aerodynamic performance of forward curved (F.C.) centrifugal fans was studied. The parameters considered are: (1) width-inner diameter ratio of impeller, (2) axial clearance between the fan inlet nozzle and the impeller shroud plate, (3) blade-setting angle, (4) blade pitch-chord ratio, and (5) spiral extension index of the scroll. Noise characteristics were evaluated by means of the specific noise level (A-weighted) at every operating point except the surging region. The optimal values for the parameters to realize low noise are discussed. Design diagrams for low noise F.C. centrifugal fans are shown.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):235-240. doi:10.1115/1.3269426.

A method is presented for the extraction of rolling bearings characteristics (stiffness and damping) under operating conditions. The method is based on experimental modal analysis combined with a mathematical model of the rotor-bearings-support system. The method has been applied for the investigation of the effect of speed, preload, and free outer race bearings on system stiffness and damping. The method proves to be very accurate for stiffness determination and reasonably so for damping.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):241-247. doi:10.1115/1.3269427.

The Rayleigh-Ritz method is applied for the damping analysis offlexural vibrations of a simply supported plate, partially covered with constrained viscoelastic damping treatment. The anaysis is carried out in terms of resonant frequencies and associated modal system loss factors. Single-term solutions for respective modes are assumed for the longitudinal displacements of the constraining layer and the transverse displacement of the plate. The variations of the resonant frequency and the associated modal loss factor with the coverage percentage, the coverage location, the core shear modulus and the thickness of the constrained and the constraining layers have been reported.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):248-254. doi:10.1115/1.3269428.

The transient responses of an elastic beam to large dynamic deformations were analyzed numerically, using the transfer matrix method. Geometrically nonlinear differential equations were linearized by introducing increments of unknown functions, and the resulting linear equations were approximated by finite difference equations. A field transfer matrix was introduced for the analyses of large deformations; this determined the relationship between the incremental state vectors at both ends of the elastic segments. The Newmark β formulation was chosen to approximate the equation of motion for concentrated masses. A concentrated mass point transfer matrix and an inhomogeneous vector were introduced for analyses of the transient responses of the beams. A superposition scheme for the transfer matrix method was proposed as an effective means of obtaining a solution satisfying the boundary conditions at both ends of the beam.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):255-261. doi:10.1115/1.3269429.

A numerical method is presented to determine the steady-state nonlinear response of a rotor-support system due to deadband and rubbing using discrete Fourier transformation and inverse discrete Fourier transformation. Damaging subharmonic and superharmonic responses are found to occur in presence of a side force. The calculated results agree with the general trends which have been observed experimentally by other investigators. The effects of selected nondimensionalized parameters on rotor response are studied.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):262-269. doi:10.1115/1.3269430.

In this paper the authors present a linear, least-squares, frequency domain filter for the identification of structural vibration parameters, such as mass, stiffness, and damping, from observed forces and responses. The method is based on an equation error formulation which produces a measurement equation which is linear in the unknown parameters. Convergence of the parameter estimates is achieved rapidly and the period required to obtain convergence is indicated by the CPU time measured on an IBM 3083 computer. Results obtained using simulated data are used to compare the linear filter with alternative filter formulations. Experimental results from a portal frame rig are given to demonstrate the application of the method to physical measurements.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):270-276. doi:10.1115/1.3269431.

A method is presented for the dynamic analysis and vibration control of large scale flexible multibody aircraft during the touchdown impacts and rollover motion. The rollover motion is simulated by modeling the uneven runway profile as a stationary zero mean space dependent random process defined by its spectral shape. The prescribed motions at the two landing gears will then represent a different time dependent random process with spectral shapes changing with the change in velocity of the aircraft. Composite materials which provide higher stiffness-to-weight ratios are used as a passive control system to reduce the aircraft vibration. The results of the numerical example presented showed that the use of composites can have a significant effect on attenuating the vibration of the aircraft during the touchdown impact and rollover motion. The numerical results are obtained using the general purpose computer program DAMS (Dynamic Analysis of Multibody System).

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):277-282. doi:10.1115/1.3269432.

In-plane stress distribution in a spinning annular disk is studied analytically. The disk is clamped at the inner boundary and subjected to a stationary distributed load along the outer boundary. The solution is determined through a Galilean transformation by using the Lamé potential functions and the two-dimensional elasticity theory. Numerical results are presented for WA vitrified grinding wheels with outer radii of 50 mm and inner radii of 25 mm rotating at 3000 rpm and 15000 rpm.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):283-288. doi:10.1115/1.3269433.

In this paper, an estimation of the stiffness matrix for a mechanical tree-like structure is presented. The coefficients of the stiffness matrix are evaluated based on Kane’s equations together with the finite segment modeling technique and matrix structure analysis. The procedure developed is used to evaluate the stiffness coefficients in the case where the flexibility effects are modeled by uniform beam elements with springs and dampers at the connecting joints. The method presented in this paper is very useful in the study of the dynamics, vibration, and control of a large tree-like structure undergoing large motions. An illustration of how the method is used in extracting the natural frequencies and their corresponding mode shapes is presented. The set of equations developed in this paper are the complement equations used to monitor the transient response of the structure undergoing a rigid-body motion.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Reliability, Stress Analysis, and Failure Prevention

J. Vib., Acoust., Stress, and Reliab. 1987;109(3):289-301. doi:10.1115/1.3269434.

This paper presents expressions for stresses in the spring due to compression or tension in the direction of the axis of the cylindrical coil. In deriving stresses in the spring, it is necessary to first obtain resultant forces and resultant moments which occur in the coil spring. Then the analysis first derives exact results based on three-dimensional curved beam theory in which all displacements and all forces in three orthogonal directions of the coil spring are included with consideration of the constraints of the ends of the spring. Since the boundary shape of the spring is irregular, it is also difficult to satisfy stress-free boundary conditions along the surface of the coil, so that this paper applies the Fourier expansion collocation method and obtains stresses in the coil spring based on the theory of elasticity.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Fastening and Joining

J. Vib., Acoust., Stress, and Reliab. 1987;109(3):302-308. doi:10.1115/1.3269435.

A semi-analytical analysis involving finite elements in conjunction with classical plate theory is used to determine the stress state in a concentrated region of the headplate on an industrial ball mill. The study illustrates the practical benefits of combining analysis techniques. With this procedure, manufacturing errors in the mill design and construction are confirmed to be a facing cut and a series of nonstructural welds on a wrapper plate between the headplate and its bearing bell mounting. The early failure of the ball mill is shown to arise from the combined detrimental effects of the residual stresses formed in the welds and groupings of broken bolts in the headplate assembly. The result, confirmed by actual site examinations, is an emphatic positive verification of the merits of hybrid analysis methods, when applied in a rational manner.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Design Technology

J. Vib., Acoust., Stress, and Reliab. 1987;109(3):309-314. doi:10.1115/1.3269436.

Grinding wheel corner wear plays a very significant role in certain cylindrical plunge grinding operations in which the corner radius is critical. The corner wear affects the tolerance specified on the plunged corner radius on the component. Monitoring of corner wear is essential to know when exactly the tolerance zone has been crossed. This paper deals with the nature and geometry of corner wear and its monitoring using the fluctuations in the airflow velocity around the grinding wheel.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Vib., Acoust., Stress, and Reliab. 1987;109(3):315-318. doi:10.1115/1.3269437.

The paper shows how unstable parametric vibrations of a uniform beam can be controlled. A control law is proposed and it is shown that the beam can be made to vibrate at a present amplitude at its natural frequency. The beam is modelled by its first mode and a solution to the governing equation of motion is derived by applying the multiple scales perturbation method. The results of the theoretical analysis are verified by a numerical simulation.

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Vib., Acoust., Stress, and Reliab. 1987;109(3):320-321. doi:10.1115/1.3269439.
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Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):321-322. doi:10.1115/1.3269440.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):322-323. doi:10.1115/1.3269441.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):323-324. doi:10.1115/1.3269442.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):325-326. doi:10.1115/1.3269443.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):326-327. doi:10.1115/1.3269444.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):327. doi:10.1115/1.3269445.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):327-328. doi:10.1115/1.3269446.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):328-329. doi:10.1115/1.3269447.
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Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):329-330. doi:10.1115/1.3269448.
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Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1987;109(3):330. doi:10.1115/1.3269449.
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Commentary by Dr. Valentin Fuster

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