In this paper, the application of the principal-component analysis method in fault diagnosis is explored. Characterized as fast and precise, this method can be directly used for analyzing gear noise and vibration signals in time domain. The principal component method and its 1 error occur-ring in the calculation are theoretically discussed in detail. A program for implementing this method has been developed and the experiments for gear fault diagnosis have been carried out with satisfactory results.

In this paper, we study the trouble diagnosis of diesel valve train by sound intensity, especially by the technique of the Gated Spectrum Analysis. To check the efficiency and reliability of our sound intensity measurement, we record vibration signals and sound intensity simultaneously to diagnose the valve train troubles of the 290-QN diesel. Some typical troubles with the valve train are analogued, the frequency spectrum plots of the vibration signals and sound intensity signals are gotten with the help of the tape recorder which record the signals in situ, so we could identify the troubles of the valve train from these frequency spectrum plots directly.

In this paper, we presented a mew mechanical model of an impact damper based on the theoretical analyses and experiments. We also presented a method of identifying the parameters of the non∼linear method of an impact system by means of microcomputer calculations. The method of identification presented in this paper has been proved byour experiments. These works supply the theoretical foundations of designing and calculating for impact damper.

Ropeways such as gondola lifts have attracted increasing interest as a means of transportation in cities. However, swing of ropeway carriers is easily caused by wind, and usually a ropeway cannot operate if the wind velocity exceeds about 15m/s. The study of how to reduce the wind-induced swing of ropeway carriers has attracted many researchers. It had been said that it was impossible to reduce the vibration of pendulum type structures such as ropeway carriers by a dynamic absorber. But in 1993, Matsuhisa showed that the swing of carrier can be reduced by a dynamic absorber if it is located far above or below from the center of oscillation. Based on this finding, a dynamic absorber composed of a moving mass on an arc-shaped track was designed for practical use, and it was installed in chairlift-type carriers and gondola type carriers in snow skiing sites in Japan in 1995 for the first time in the world. It has been shown that a dynamic absorber with the weight of one tenth of the carrier can reduce the swing to half. The liquid dynamic absorber was also investigated. It has the same damping effect as the conventional solid absorber. It is easy to adjust the natural frequency and the damping ratio, and the structure is simple. Therefore, it will be applied for not only ropeway carriers but also ships and rope suspended bridge and others.

This paper investigates the nonlinear dynamic response of a linearly elastic string fixed at one boundary and undergoing constant speed circular motion at the other boundary. The response divides into nonlinear, steady state ballooning that is fixed relative to a rotating coordinate system and linearized vibration about the steady state. Single loop balloons have high tension and purely imaginary eigenvalues. The single loop vibration frequencies generally decrease with increasing balloon length. Highly extensible strings whirl in first and higher modes with forward whirling modes having lower frequencies. Axially stiff strings exhibit whirling only in higher modes. If the nondimensional string stiffness is larger than 1000 then the inextensible steady state solutions and the lowest six vibration frequencies match the extensible results to within 3%. One and a half loop balloons are divergently unstable. Long and/or sufficiently extensible strings form low tension double loop balloons. Inextensible double balloons are coupled mode flutter unstable. The steady state balloons, steady state eyelet tension, and balloon stability are experimentally verified.

Ritz vectors offer many advantages over the traditional mode shapes in the areas of model reduction and structural dynamic simulation. Building upon the recent development of an experimental method to extract Ritz vectors from measured dynamic response data, these vectors were also demonstrated to offer great potential in the areas of finite element model correlation and structural damage detection. In this paper, a Monte Carlo simulation is performed to study the accuracy and stability of Ritz vectors extracted from this new procedure using noise corrupted response data. The statistical variation of Ritz parameters and modal parameters extracted from the same data is made to assess the sensitivity of Ritz vector extraction to measured noise.

The stiffness, first mode natural frequency and deflection profile can be used to describe the performance of a fly rod. A finite element model has been developed which predicts the performance parameters of fly rod blanks as a function of the geometry and material properties of the blanks. The results of the model compare favorably with experimental results. The model was used to evaluate the effects of changes of design parameters on rod performance. The natural frequency of a rod or a rod blank is a function of the stiffness to mass ratio and the mass distribution of the rod. An empirical equation that predicts the natural frequency of a rod or a rod blank as a function of the mass of the tip section, location of the center of gravity of the tip section and rod stiffness is presented. The line weight rating for fly rods was found to be a function of the stiffness and frequency of the rods. For the first time, an empirical method for the selection of a line weight that matches the performance characteristics of a rod is presented.

Vibration generated by underground railways is difficult to control because of the very limited space available in a tunnel. A popular approach is to use ‘floating slab track’ whereby the rails are fixed to a large concrete foundation separated from the tunnel wall by a resilient material. This paper investigates some of the vibration characteristics of floating slab track from measurements made in situ. These measurements are compared with the theoretical response of an infinite beam on an elastic foundation taking into account the torsional response of the beam. The transmission of vibration through the tunnel wall and into the surrounding medium is discussed with reference to the relative speed of travelling waves and the coincidence frequencies.

Placement and orientation of fasteners in assemblies is generally based on convenience or static load and strength considerations. Vibration and other dynamic loads can result in loosening of threaded product, particularly when cyclic shear stresses are present. This paper investigates the placement of a bolt and nut on a compound cantilever beam subjected to dynamic inertial loading. Calculations for an inertial loaded, cantilever, Euler-Bernoulli beam show that the dynamic shear stress is maximum near the dynamic nodal lines, and essentially vanishes near the anti-nodes. Experiments with a compound cantilever beam assembly with one fastener reveal that loosening occurs more readily when the bolt and nut are placed near a nodal line. Data presented include time to loosen, break-away torque, and acceleration level. The data shows that fastener integrity is maintained for longer periods of time and with lower tightening torques, when the bolt and nut are positioned away from nodal lines where shear stresses are lower, even though acceleration levels are higher.

Several experiments and analyses have carried out in the field of brake squeal and there are many suggestions to be found in the literature as to the cause of brake squeal. In this paper a mathematical model for friction-induced vibration and noise generation is used to study the influence of these different squeal excitation types. Squealing brakes are excited by the friction forces in the interface between the drum and the linings. This friction and its interaction with the brake structure can be modeled in many different ways. In this paper, different self-excitation types identified in the literature are tested — each one having the potential of generating instabilities. The drum brake model used for the analysis is two-dimensional, and consists of a drum and two shoes with linings. The same brake geometry and material properties are used for all computations, which means that the influence of each mechanism can be estimated. The results from this analysis show that, among the friction models analyzed, the constant coefficient of friction model gives the largest contribution to the instability level of squealing drum brakes. The contribution from the negative μ-velocity slope is shown to be minor. For the constant coefficient of friction model, there are different excitation types. Among these, lining deformation induced instabilities are shown to generate large instabilities, follower forces show a negligible contribution to the instabilities generated and self-locking is shown to be impossible for the brake analyzed.

This paper describes a self-excited vibration model of dragonfly’s wing based on the concept of bionic design, which is expected as a technological hint to solve the scale effect problems in developing the small- or micro-sized actuators. From a morphological consideration of flight muscle of dragonfly, the nonlinear equation of motion for the wing considering the air drag force due to flapping of wing is formulated. In the model, the dry friction-type and Van der Pol-type driving forces are employed to power the flight muscles and to generate the stable self-excited wing vibration. Two typical Japanese dragonflies, “Anotogaster sieboldii Selys” and “Sympetrum frequens Selys”, are selected as examples, and the self-excited vibration analyses for these dragonfly’s wings are demonstrated. The linearized solutions for the nonlinear equation of motion are compared with the nonlinear solutions, and the vibration system parameters to generate the stable limit cycle of self-excited wing vibration are determined.

Brake judder can be explained as a dynamical amplification of brake torque variation (BTV) when passing through a critical speed of a vehicle. The BTV arises owing to different geometrical defects e.g. disc thickness variation (DTV), disc runout and dynamical effects. DTV is usually the most important source of these fluctuations. Measurements have been made on a passenger car with heavy DTV on one of its front brakes. The eigen frequency of the wheel suspension was found to be 14 Hz, corresponding to a first order critical speed of 95 km/h. These measurements qualitatively verify the brake model with a maximum caliper vibration amplitude close to 100 km/h followed by a slowly decreasing amplitude.

The fundamental issue confronting a vibration test engineer is how to obtain the best representation for the natural frequencies and corresponding mode shapes of a mechanical system. In the case of a structure such as a vehicle that has rigid body degrees of freedom, a vibration test requires some sort of artificial support system. The purpose of this work is to quantify the influence of this support system using two example structures: a one-degree-of-freedom oscillator, and a uniform beam on two types of supports. In all cases, the actual influence of the supports on the modal test results is greater than one would estimate a priori. It is hoped that these results, which have been derived from exact solutions, will provide insight for designing test supports for more complex structures.

Stepped thrust gas film bearings are widely used for high speed rotating machinery because of their simple structure, relatively high load carrying capacity and stability. In such bearings, the gas film inertia forces may play an important role under high speed conditions. In this paper, the vibration analysis of high speed, stepped thrust gas film bearings considering the inertia effects is described. In the numerical analysis, the static and dynamic pressure distributions in pocket and land regions are evaluated from the generalized Reynolds equation considering the centrifugal force. The pressure values at the step are calculated by considering the conservation of mechanical energy and the continuity of gas film flow in pocket and land regions. Moreover, the dynamic response of bearings subjected to impulsive and sinusoidal excitations are analyzed for different values of film thickness ratios. From the numerical results, the effects of gas film inertia on the vibration characteristics of bearings are clarified.

This paper describes the influence of bearing alignment (vertical position) on vibration of multi-rotor-bearing system. The rotor-bearing system used in this study consists of three rotors and six bearings. It is designed to have the equivalent dynamic characteristics to the turbo-generator-systems for utility power generation plant. And it is equipped with alignment setting devices which can set the bearing alignment in vertical direction precisely without disassembling the test rig. It was confirmed that bearing alignment affects the rotor vibration. Some critical speeds and their peak amplitudes change. When the bearing alignment changes, the load of the bearing changes and it affects oil film characteristics. The calculated results considering this agree with the test results. The effect of the bearing alignment on the rotor vibration becomes large when the bearing load is about zero.

A new design strategy of gear system is proposed in this paper. Traditionally, development of gear systems undergoes as such. First gear structural parameters are determined. Then control of dynamic behaviours such as control of vibration is dealt with, where gear structural parameters cannot be changed any more. The new strategy suggests that during the design process of determining gear structure parameters, vibration control is taken into account. In order to see the effects of such a design strategy, an optimal design model is developed which contains two conflicting objectives, system vibration and system volume. The design variables include both discrete ones and continuous ones. Genetic algorithm, together with Pareto sets, is employed to solve this complex optimal problem. Through the simulation studies on selected cases, improvement on the system vibration control is shown with this new design strategy.

Recently, several new machining techniques have been developed which have driven dramatic changes in the manufacture of aerospace components with thin ribs and webs. There are many such components in commercial and military aircraft, and until recently these components we fabricated as sheet metal assemblies. Through an improved understanding of the dynamic interaction between the tool and workpiece, it has now become economically competitive to create components with thin ribs and webs as monolithic units machined from a solid block by milling. Ribs are those thin structures created at the periphery of the end mill, as opposed to webs, which are the thin structures created at the face of the end mill. It is easy to see that as the ribs and webs become thinner, the stiffnesses will decrease, and chatter will become more problematic. Chatter during the machining of such parts can result in damage to the part (even cutting through the thin structure) or at least poor surfaces which require hand finishing. This paper outlines the basic technology required to produce these kinds of components efficiently, and cites several examples.

The method of direct separation of motions and the general approach, called by the author “vibrational mechanics”, is developed so as to fit the problems of the effect of vibration on systems with dry friction and shock. The main idea of this approach lies in the transfer from the initial system of differential equations to the system, describing only the slow components of motion, most interesting for applications. It is these equations that are called the equations of vibrational mechanics. The advantages of this approach are especially significant in the case of systems with dry friction (Coulomb friction) and with unilateral constraints whose presence in case of vibration leads to multiple collisions of the system bodies. Instead of the not smooth system or with the discontinuous right sides there is a “smooth” system often of a lower order; an essentially non-potential system may be answered by a potential system. Methods and approaches presented in the report are illustrated by the solution of two applied problems — a simplest problem of the transportation of a body along a rough vibrating surface and a problem on the motion of a body in space between the vibrating surfaces under periodic impacts. A short reference of investigations is given where the proposed approach is used or can be used quite effectively. In conclusion the main regularity is formulated which characterizes the action of vibration on systems with dry friction and impacts.

In ground vibration testing of flexible missiles to determine their in-flight vibration modes, it is desirable that the support stiffness be as small as possible relative to the missile beam stiffness. This paper analyzes the effect of a rotational stiffness applied to one end of a uniform free-free beam. The changes in the natural frequency and node locations for the first two modes are calculated as a function of the support stiffness. The Saturn V Apollo Launch Vehicle is used as a numerical example.

A wire nail production machine can be classified as one of the punch press machines. By nature, the production of wire nails involves the development of a series of force impulses which in turn generate various sound pressure levels with different frequencies. Typically, the machine operations generating impact noise include pressing, cutting, ejecting, wire gripping and feeding. The punch pressing is the movement of punch header to press forming the nail head. It produces a large force impulse which in turn generates a high level of impact noise and consequently high levels of ancillary impact noise such as the impact noise by the backlashes. It has been found that this type of impact noise is not necessarily the most annoying one. The impact noise generated by nail ejection, however, has been identified as one of the annoying noise components. The ejector used in a nail machine for executing the movement of nail ejection produces ringing noise at high frequencies when it is struck by the punch header in each cycle of the machine operations. This paper presents the analyses of and experiments on the ejection force impulse and the characteristics of the impact noise generated by nail ejection.