A study of hand vibration on chipping and grinding operators,part III: Power levels into the hands of operators of pneumatic tools used in chipping and grinding operations

This paper presents a method for calculating power transmitted to the hands of operators who use vibrating hand tools. Results that relate to a comprehensive multidisciplined NIOSH field study of several hundred chipper and grinder workers who used pneumatic hand tools are presented. The results of this study indicated that the power in the frequency range of 6·3 Hz to 1000 Hz transmitted to the hand ranged from 1·08 × 10³ to 7·23 × 10³ J/s for the chisel and from 8·52 × 10^?1 to 1·57 × 10² J/s for the handle of chipping hammers. For pneumatic grinders the power transmitted to the hands of the tool operators was in the range of 6·58 × 10^?3 to 2·35 × 10^?3 J/s over the same frequency range.     

A study of hand vibration on chipping and grinding operators,part I: Vibration acceleration levels measured on pneumatic tools used in chipping and grinding operations

This paper describes the acceleration measurements and data analysis aspect of a comprehensive multidisciplined field study of several hundred chipper and grinder workers using pneumatic hand-held tools. Engineering testing of a sampling of these tools indicated that for a frequency range of 6·3 Hz to 1000 Hz, overall acceleration levels between 2000 m/s² and 24 000 m/s² were measured on the chisels and levels between 37 m/s² and 350 m/s² were measured on the handles of chipping hammers. Hand grinder acceleration levels ranged from 6 m/s² to 21 m/s².     

Hand-arm vibration part III: A distributed parameter dynamic model of the human hand-arm system

An anatomically analogous distributed parameter dynamic model of the human arm is proposed and quantitatively validated. Distributed mass and stiffness parameters have been obtained by representing each long bone of the arm as a flexural beam. A distributed damping parameter was introduced by allowing the beam stiffness to be a complex quantity. Hand properties were modelled as a lumped parameter damped spring-mass system. Mechanical driving point impedance techniques were used to verify the model. A dual beam model of the forearm was first proposed, and its frequency response was compared with impedance data collected on the forearm. After having established the validity of the forearm model, it was then extended to include the upper arm. The frequency response of the whole-arm model was then compared with impedance data on the whole arm collected by a previous investigator. It is concluded that the beam model of the human arm adequately represented its dynamic behavior as measured by mechanical driving point impedance techniques. The amount of information concerning the dynamic behavior of the arm yielded by the distributed parameter model is found to be vastly greater than that yielded by lumped parameter models.     

Whirling and stability of flywheel systems,part II: Comparison of numerical results obtained with combined and lumped parameter models

In this paper the theoretical analyses of Part I are applied to some flywheel systems to provide information to designers. The analyses are utilized to study three specific prototype flywheel systems: a multi-material ring type (Garrett AiResearch), a constant-thickness-disk ring type (General Electric), and a tapered-thickness-disk type (Lawrence Livermore National Laboratory). In addition, the effects of the following flywheel design parameters on system dynamics are investigated: flywheel mass, flywheel diametral and polar mass moments of inertia, location of flywheel diametral and polar mass moments of inertia, location of flywheel mass center from the lower end of the quill shaft, quill shaft length, lower turbine-bearing support stiffness, and equivalent viscous damping coefficient of the external damper.     

A phenomenology of boundary lubrication: the lumped junction model

We propose a phenomenological model of boundary lubricated junctions consisting of a few layers of small molecules which describes the rheological properties of these sytems both in the static, frozen, and sliding, molten, states as well as the dynamical transition between them. Two dynamical regimes can be distinguished, according to the level of internal damping of the junction, which depends on its thickness and on the normal load. In the overdamped regime, under driving at constant velocity v through an external spring, the motion evolves continuously from “atomic stick-slip” to modulated sliding. Underdamped systems exhibit, under given external stress, a range of dynamic bistability where the sheared static state coexists with a steadily sliding one. The frictional dynamics under shear driving is analyzed in detail, it provides a complete account of the qualitative dynamical scenarios observed by Israelashvili et al., and yields semiquantitative agreement with experimental data. A few complementary experimental tests of the model are suggested. Received: 18 December 1997 / Received in final form and accepted: 26 March 1998     

Dynamic response of composite plates with cut-outs,part II: Clamped-clamped plates

The forced and free dynamic response of plates with cut-outs formulated in Part I [1] is used to investigate the effect of cut-outs on the natural frequencies of clamped-clamped plates. The size, shape and location of the cut-out is expressed as a displacement dependent external loading. The plates considered are homogeneous and anisotropic. Lagrange's equations of motion lead to an infinite system of differential equations in time-dependent generalized co-ordinates with generalized forces which include the effects of the cut-outs. There is an infinite system of frequency equations for free vibrations. The infinite system is truncated to a finite system of equations depending upon the accuracy desired in frequency values. Results are given for square, clamped-clamped plates with centrally located square cut-outs for different modulus ratios. Good agreement is obtained when results for isotropic plates with cut-outs are compared with available theoretical and experimental results.     

Propeller aircraft interior noise model,part II: Scale-model and flight-test comparisons

Part I [1] of this paper contains the theory used to create a basic propeller aircraft interior noise model. The model predicts tonal levels of blade passage harmonics in the cabin of a propeller driven aircraft. Part II presents the results of validation studies based on scale-model and flight comparisons.     

Realisations of the representations of para-Fermi algebra in Fock space of Bose operators: part II

Using the method given in Part I of this series (this volume, pp. 109–114), Green's isomorphisms of the para-Fermi algebra F _2n ¹ with 2n generators into ∈ _2n+1 ^a(2) are constructed. All the representations of the para-Fermi algebra are realised in Fock space #x210B; _2n ¹ of 2ⁿ Bose opcrators.     

The vibration and post-buckling of geometrically imperfect,simply supported,rectangular plates under uni-axial loading,part II: Experimental investigation

The paper describes the experimental part of a theoretical and experimental study of the post-buckling and free vibrational behaviour of thin, rectangular, simply supported plates having initial geometrical imperfection and subject to uni-axially applied, in-plane, compressive loads. The experimental apparatus and procedure used are described. The fundamental natural frequency and central deflection of several plates of different thickness and degree of initial imperfection, subject to loads varying from zero to several times the critical buckling value, are compared with values predicted by using the Rayleigh-Ritz solution described in the companion paper. For one plate, comparisons of theoretically predicted and experimentally measured strains are given. Close agreement is shown to exist between the theoretical and experimental results. An approximate linear relationship between a load-frequency parameter and the central deflection, discussed in the theoretical study, is also shown to exist for the experimental plates.     

腔壁弹性对充水亥姆霍兹共振器声学特性的影响:圆柱形腔等效集中参数模型

研究了充水亥姆霍兹共振器的弹性壁对其声学特性的影响。建立了考虑壁面弹性的圆柱形共振器的等效集中参数理论模型,并在静水管路上进行了实验验证。从共振器的共振频率、激励声压与腔内声压的传递函数以及共振器的传递损失等方面阐述了弹性壁的影响,并对刚性壁假设和弹性壁结果进行了比较。理论和实验都证明了腔壁弹性对亥姆霍兹共振器的声学特性有很大的影响。     

Determination of the inhomogeneous structure of a medium from its plane wave reflection response,part II: A numerical approximation

This paper is concerned with a standard one dimensional inverse scattering problem: given the reflection response of an unknown inhomogeneous medium for plane waves under normal or oblique incidence, determine its sound speed and density structures. The problem is solved by means of a simple numerical technique which involves only fast Fourier transform operations and numerical integration of ordinary differential equations. Three cases are specifically considered: (a) sound speed is unknown, density is known; (b) sound speed is known, density is unknown; (c) sound speed and density are to be determined simultaneously. Numerical simulations performed on reflection coefficients computed in Part I for a limited band of frequencies lead to accurate reconstructions of the original structures of various media.     

A model of classical thermodynamics and mesoscopic physics based on the notion of hidden parameter,Earth gravitation,and quasiclassical asymptotics. II

This paper presents a new approach to thermodynamics based on two “first principles”: the theory of partitions of integers and Earth gravitation. The self-correlated equation obtained by the author from Gentile statistics is used to describe the effect of accumulation of energy at the moment of passage from the boson branch of the partition to its fermion branch. The branch point in the passage from bosons to fermions is interpreted as an analog of a jump of the spin. A hidden parameter–the measurement time as time of the G¨odel numbering–is introduced.     

Influence of parameter estimation on integrated backscatter: a model study

This paper studies the influence of parameter estimation on integrated backscatter using a computer model. The study is specifically aimed at applications to the heart muscle; however, the validity of the conclusions drawn from this work should be confirmed by in vivo tests.     

The apparent mass and mechanical impedance of the hand and the transmission of vibration to the fingers, hand, and arm

Although hand-transmitted vibration causes injury and disease, most often evident in the fingers, the biodynamic responses of the fingers, hand, and arm are not yet well understood. A method of investigating the motion of the entire finger-hand-arm system, based on the simultaneous measurement of the biodynamic response at the driving point and the transmissibility to many points on the finger-hand-arm system, is illustrated. Fourteen male subjects participated in an experiment in which they pushed down on a vertically vibrating metal plate with their right forearm pronated and their elbow bent at 90°. The apparent mass and mechanical impedance of the finger-hand-arm system were measured for each of seven different contact conditions between the plate and the fingers and hand. Simultaneously, the vibration of the fingers, hand, and arm was measured at 41 locations using a scanning laser Doppler vibrometer. Transmissibilities showed how the vibration was transmitted along the arm and allowed the construction of spectral operating deflection shapes showing the vibration pattern of the fingers, hand, and arm for each of the seven contact conditions. The vibration patterns at critical frequencies for each contact condition have been used to explain features in the driving point biodynamic responses and the vibration behaviour of the hand-arm system. Spectral operating deflection shapes for the upper limb assist the interpretation of driving point biodynamic responses and help to advance understanding required to predict, explain, and control the various effects of hand-transmitted vibration.     

A lumped mucosal wave model of the vocal folds revisited: recent extensions and oscillation hysteresis

This paper examines an updated version of a lumped mucosal wave model of the vocal fold oscillation during phonation. Threshold values of the subglottal pressure and the mean (DC) glottal airflow for the oscillation onset are determined. Depending on the nonlinear characteristics of the model, an oscillation hysteresis phenomenon may occur, with different values for the oscillation onset and offset threshold. The threshold values depend on the oscillation frequency, but the occurrence of the hysteresis is independent of it. The results are tested against pressure data collected from a mechanical replica of the vocal folds, and oral airflow data collected from speakers producing intervocalic /h/. In the human speech data, observed differences between voice onset and offset may be attributed to variations in voice pitch, with a very small or inexistent hysteresis phenomenon.     

Network-theoretical model of the gyrotron oscillator part II: Empty cavity oscillation modes

A network-theoretical model of the gyrotron has been elaborated which is both conspicious and rigorous. The electromagnetic field in the presence of the electron beam, to be determined in a self-consistent calculation, might be regarded as an abstract vector in infinite-dimensionalHilbert space. In the first part of this paper, a method was described to determine the oscillation modes of empty gyrotron cavities. Once these oscillation modes are known, their fields can be used as the coordinate system for the representation of this vector. In this representation,Maxwell's equations reduce to a system of ordinary differential equations — the so-called resonator equations, describing the linear dependence of the field amplitudes on the excitation coefficients. They are readily solved in the frequency domain. The solution can be represented as a parallel resonance circuit, if the mode amplitudes are identified with equivalent voltages, and the exciation coefficients with equivalent currents.The nonlinear dependence of the excitation coefficients on the mode amplitudes, on the other hand, is then identified with the device (or electron beam) admittance. The latter is determined numerically, for a number of points in the amplitude-frequency plane, and subsequently represented in the frequency domain. In order to efficiently compute the device admittance, the coordinates are transformed into the electron beam frame, and afterwards an averaging method is applied. The interaction of these admittances determines the behaviour of the gyrotron.