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BOOK REVIEWS

J. Vib., Acoust., Stress, and Reliab. 1983;105(3):267. doi:10.1115/1.3269097.
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Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):267-269. doi:10.1115/1.3269098.
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Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):269-270. doi:10.1115/1.3269099.
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Abstract
Topics: Acoustics
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Design Technology

J. Vib., Acoust., Stress, and Reliab. 1983;105(3):274-279. doi:10.1115/1.3269100.

This paper is concerned with instability of a rotor that arises due to fluid film forces of a journal bearing. The half frequency whirl and the resulting oil whip phenomena is explained by a consideration of flow balance in a bearing which looses the load carrying capacity. The threshold instability criterion for a rigid rotor in plain cylindrical bearings is given in the form of a chart by obtaining the solution of equations of motion with the corresponding spring and damping coefficients. Both translatory and conical whirls are considered. The analysis is then presented for a flexible rotor and a simple procedure is given to obtain the instability threshold speed based on the rigid rotor criterion. The procedure does not involve any trial and error iteration calculations and is illustrated by a case study.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):280-285. doi:10.1115/1.3269101.

Described in this paper is an approximate technique for the simulation of a mechanical feature pattern gage (a go/no-go gage). The procedure involves the unconstrained minimization of a judiciously constructed response function. The formulation of this function as well as the development of the associated algorithm are presented. Moreover, the technique is demonstrated on an assortment of sample problems.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):286-291. doi:10.1115/1.3269102.
Abstract
Topics: Stress , Design , Nozzles
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):292-299. doi:10.1115/1.3269103.

Reduced computing costs and continued development of computational methods of heat transfer make it possible to simulate complicated heat sealing processes on a computer. Such a simulation is developed for an impulse heat sealing machine and is used for a parametric study of the magnitude and duration of the heat pulse and the length of time the clamping jaws remain closed after the heating period ends. The results (i.e., the temperatures at critical points in the material being sealed) are shown to be useful in setting initial design specifications for the impulse heat sealer.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):300-304. doi:10.1115/1.3269104.

Regenerative braking (RB) systems have existed in conceptual form for several years. The present work develops calculations which demonstrate the practicality of such systems. It is shown that fuel savings of from 4.3 to 8.5 percent are achievable, leading to a reduction in transportation petroleum consumption of about 8.1 × 109 l/yr in the U.S. alone.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):305-311. doi:10.1115/1.3269105.

This paper presents a direct method for determining the geometry factor J for slotted external spur gears. The location of maximum stressed point on the tooth profile where the stress parabola is tangent to the fillet curve has been determined by solving the resulting nonlinear equations using the sophisticated Newton-Raphson method. The semi-graphical procedure given in AGMA Standard [1] is not convenient for determining the geometry factory J of large gears used in grinding mill and kiln drives in the mining industry. Listing of the computer program and input-output point out for a typical application are presented.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):312-316. doi:10.1115/1.3269106.

This paper describes the design concept of a new robot based on the direct-drive method using rare-earth d-c torque motors. Because these motors have high torque, light weight and compact size, we can construct robots with far better performance than those presently available. For example, we can eliminate all the transmission mechanisms, such as reducers and chain belts, between the motors and their loads, and construct a simple mechanism (direct-drive) where the arm links are directly coupled to the motor rotors. This elimination can lead to excellent performance: no backlash, low friction, low inertia, low compliance and high reliability, all of which are suited for high-speed, high-precision robots. First we propose a basic configuration of direct-drive robots. Second a general procedure for designing direct-drive robots is shown, and the feasibility of direct drive for robot actuation is discussed in terms of weights and torques of joints. One of the difficulties in designing direct-drive robots is that motors to drive wrist joints are loads for motors to drive elbow joints, and they are loads for motors at shoulders. To reduce this increasing series of loads is an essential issue for designing practical robots. We analyze the joint mass system for simplified kinematic model of the direct-drive robots, and show how the loads are reduced significantly by using rare-earth motors with light-weight and high torque. We also discuss optimum kinematic structures with minimum arm weight. Finally, we describe the direct-drive robotic manipulator (CMU arm) developed at Carnegie-Mellon University, and verify the design theory.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):317-320. doi:10.1115/1.3269107.

The optimum design of an one-dimensional cooling fin is considered by including all modes of heat transfer in the problem formulation. The minimum principle of Pontryagin is applied to determine the optimum profile. A new technique is used to solve the reduced differential equations with split boundary conditions. The optimum profile found is compared with the one obtained by considering only conduction and convection.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Vibration and Sound

J. Vib., Acoust., Stress, and Reliab. 1983;105(3):321-325. doi:10.1115/1.3269108.

This paper deals with the stability of motion of an elastically suspended vibrating hammer that impacts upon an energy absorbing surface referring to the dynamical interaction between a vibrating hammer and a motor. Assuming an ideal source [1] of energy is characteristic of a motor, then the force mr ω2 cosωt appears to be the vertical component of the inertia force of the mass m . The mass m is located the distance r from the axis 0 and rotates by frequency ω. Hence the basic equation of a vibrating system takes the form of a linear system. Fu [2] has investigated the regions of stability of the system as the linear system. In the case of practical use, however, a limited power source called a “nonideal source of energy” is the characteristic of a motor. Accordingly, it follows that the motion of an oscillating system with a nonideal source of energy may be formulated as a nonlinear system. The local stability of the sytem desired by a nonlinear equation is presented in our paper. Finally, the results of the regions of stability are compared with those studied in Fu.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):326-331. doi:10.1115/1.3269109.

Stability bounds are outlined for the null solution of the equation describing the response of a linear damped oscillator excited through periodic coefficients, the excitation being a form of Rice noise comprising equal amplitude sinusoids with frequencies at equal intervals in the vicinity of twice the natural frequency of the system, but with pseudo-random initial phases. Stability was investigated by the monodromy matrix method, which is exact apart from errors due to numerical integration, and by the approximate method due to R. A. Struble, which replaces the dependent variable by its amplitude and a phase variable. Struble’s method gives the main features of the stability diagram and leads to faster and more robust numerical integration with potential advantages for nonlinear and several degree-of-freedom systems, but loses much of the detail. When the frequency spacing is relatively large, the stability diagram is closely related to that for Mathieu’s equation, but the detailed shape becomes very complicated as the frequency spacing decreases. Quantitative comparison with the corresponding boundary for Gaussian white noise excitation shows very approximate equivalence.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):332-336. doi:10.1115/1.3269110.

An approximate solution procedure is presented for a class of steady vibro-impact problems consisting of adjacent structures separated by a gap and subjected to harmonic base excitation. The procedure is based on a weighted mean-square linearization technique, and is capable of substantial reduction of computational effort over that required for an exact numerical simulation. As an illustration of the general approach, a detailed analysis of an example problem is presented, together with a comparison of results with an exact solution. It is shown for the example problem that the level of accuracy of the approximate solution is adequate for many applications.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):337-344. doi:10.1115/1.3269111.

In the high frequency range of vibration the Statistical Energy Method provides one of the most convenient ways of estimating vibration levels in structural components. The dynamic characteristics of the structure are described in terms of the modal densities, dissipation loss factors and coupling loss factors of the component parts. Theoretical and semiempirical results are available for some typical components. This paper describes the development of indirect methods for the experimental determination of these three parameters. Where theoretical results are available the experimental results show reasonable agreement. The results of tests on a range of components are described.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):345-354. doi:10.1115/1.3269112.

An experimental study of the fluctuating velocity field and the fluctuating static wall pressure in an annular turbulent air flow system with a radius ratio of 4.314 has been conducted. The study included direct measurements of the mean velocity profile, turbulent velocity field and fluctuating static wall pressure from which the statistical values of the turbulent intensity levels, power spectral densities of the turbulent quantities, and the cross-correlation between the fluctuating static wall pressure and the fluctuating velocity field in the core region of the flow were obtained. The effect of the turbulent core region of the flow on the wall pressure fluctuations was studied by cross-correlating the axial and radial velocity components with the wall pressure fluctuations. A three-sensor, signal subtraction data analysis method using coherence techniques was developed to separate the superimposed local pressure fluctuations and acoustically transmitted noise. This analysis method is shown to adequately isolate the local pressure fluctuation information at each wall of the flow channel. The results of the experimental measurements are compared with existing experimental and numerical information on turbulent annular flow fields and wall pressure statistics. The pressure-velocity correlation indicates that a substantial contribution to the pressure field on the wall of the flow channel is from the turbulent core region outside of the boundary layer. The wall pressure field is shown to be significantly different on the two dissimilar walls. The pressure-velocity correlations show that this difference is due to the geometric difference between the dissimilar volumetric sources which contribute to the wall pressure field. The results of this study show that vibration modeling must incorporate the effects of the flow geometry on the wall pressure statistics, which are used as the driving force for flow-induced vibrations.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):355-360. doi:10.1115/1.3269113.

Flow in an annular passage is a common feature in the fuel channels of the UK Advanced Gas Cooled Reactors, and in some cases has required investigation to avoid or reduce flow-induced vibration of reactor components. A number of studies have been made of vibration induced by annular flow, and these are briefly reviewed in the first part of this paper to provide some background to the topic. The second part of the paper goes on to describe the investigation of the most recently recognized problem of this type, which is a flow instability caused by a diameter reduction of limited length in a long annulus. A method of eliminating the mechanism is also described.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):361-368. doi:10.1115/1.3269114.

Using the concept of force generators, various active vibration configurations have been examined for their performance potential. It is shown that an active vibration control system offers a great deal of flexibility in that by a proper choice of active components its transmissibility characteristics can be altered to suit the requirements. It is also shown how the full potential of active systems can be achieved even when there are passive components. An active system is designed in such a way that it gives the desired performance even in the event of the failure of the active components through the reliability offered by a passive system.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):369-373. doi:10.1115/1.3269115.

The most significant source of damping inherent in a structure is that damping which occurs in the structural joints due to interfacial slip. Thus, particular emphasis should be put on controlling and increasing the damping which occurs in these joints if the dynamic response, stress, and noise of a structure are to be reduced. It is shown that an optimum joint clamping force exists for maximum energy dissipation due to slip, and that the resonance frequencies of structures can be controlled to some extent by adjusting the clamping and, hence, the slip, in joints. The application of joint damping to beam-like structures, plates, and frameworks is considered, and its effect on the vibration of these structures discussed.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):374-381. doi:10.1115/1.3269116.

In this paper, we deal with the problem of active damping of vibrations of a continuous viscoelastic structure, and a general method of computation of the control system is developed. We define a mechanical model for this structure, the sources of perturbing vibrations, the control system, and different absorption criteria. The problem is set in an infinite dimension space, and an approximation problem is derived in n dimension spaces. Two methods of resolution are proposed for this approximation problem, and the solutions are compared. An example is given for the case of flexural vibrations in beams. Numerical results simulating the behavior of flexural vibrations in a rectangular plate, which is simply supported along the whole boundary, are presented for three different absorption criteria, thus permitting a quick evaluation of the comparative effectiveness of the chosen criteria.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):382-392. doi:10.1115/1.3269117.

The study of nonlinear damping in vibrations is motivated by the desire to represent and predict real responses more accurately than allowed by the limitations of linear analysis, since observed phenomena are, in general, actually nonlinear in nature. The scope of this paper is to compare the normal engineering methods of including the effects of nonlinear damping to more exact methods of solution so that the range of applicability of the normal methods may be known and the limitations of linear analysis more fully understood.

Topics: Damping , Vibration
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):393-401. doi:10.1115/1.3269118.

Noise from high-speed machine systems is an important engineering design problem. This study investigates a recently developed analytical technique for calculating the noise generated by linkage-type machines based both on recently developed analytical methods for modeling the dynamic response of machines and on classical acoustical theory. This acoustical-dynamic modeling method is applied to an experimental system with elastic elements and clearance connections; the analytically predicted acoustical fields are compared to the measured noise. The results show excellent correlation between the experimental and analytical noise fields and support the validity of this modeling method.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1983;105(3):402-407. doi:10.1115/1.3269119.

This paper presents the results of an investigation addressing the effects of mistuning on the lower modes of vibration of a simple bladed-disk model. The phenomena of dual modes, also known as mode splitting, is studied using holographic interferometry and strain gage measurements under nonrotating and rotating conditions. Resonant amplitudes, mode shapes, and natural frequencies of the disk model were determined, without deliberately mistuning the disk. The tests were then repeated with the disk deliberately mistuned to varying degrees, paying particular attention to the second diameter (2N) dual modes. Additionally, tests were conducted on the disk at a rotational speed of 2000 rpm, in an effort to gain insight as to the vibratory characteristics of the disk under rotating conditions.

Commentary by Dr. Valentin Fuster

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