5,993 research outputs found
Selected papers on some research in the vibration control field during the period 1967 to 1990
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Vibrational power transmission in curved beams
No full textPrevious research into structural vibration transmission paths has shown that it is possible to predict vibrational power transmission in simple beam and plate structures. However, in many practical structures transmission paths are composed of more complex curved elements; therefore, there is a need to extend vibrational power transmission analyses to this class of structure. In this paper, expressions are derived which describe the vibrational power transmission due to flexural, extensional and shear types of travelling wave in a curved beam which has a constant radius of curvature. By assuming sinusoidal wave motion, expressions are developed which relate the time-averaged power transmission to the travelling wave amplitudes. The results of numerical studies are presented which show the effects upon power transmission along a curved beam of: (i) the degree of curvature; and (ii) various simplifying assumptions made concerning beam deformation
A new measurement technique for the estimation of core shear strain in closed sandwich structures
No full textSandwich structures have been widely used for many years in applications such as aircraft panels, marine-craft hulls, racing car bodies and spacecraft solar arrays. Most sandwich panel designs include a lightweight core such as paper honeycomb or closed cell foam encased between two face plates, and in the case of aircraft panels constructed from carbon fibre reinforced plastics, the core is bevelled and edge pan plies are included to totally enclose the core. This type of design restricts access to the core making it almost impossible for the engineer to measure the shear strain developed in the core during in-service static or dynamic loading. This paper introduces a new measurement technique whereby the shear strain in the core can be estimated from face plate measurements using a linear finite difference approximation. The estimation method is presented and supported by calculations on a statically loaded sandwich beam. Static and dynamic experiments were conducted in order to validate the technique using a honeycomb sandwich beam instrumented with strain gauges on the core and face plates. The results showed excellent agreement between measured and estimated core shear strain for sandwich configurations with thin face plates, such as those encountered in aircraft and marine-craft constructions
Free vibration of doubly curved composite honeycomb rectangular sandwich panels
No full textSandwich panels have a wide variety of applications in many branches of engineering including aerospace, marine, civil and motorsport. Their very high stiffness-to-weight ratio make them particularly useful in aircraft and typical applications include floor panels, fairings and inlet cowl panels. In the latter case, the geometry of the panels can be considered doubly curved and they are usually constructed with carbon fibre reinforced plastic face plates and a lightweight resin impregnated paper honeycomb core. The free vibration of such panels both experimentally, and theoretically using a commercially available finite element code, has been investigated. Results are presented for the natural frequencies, and the theoretical investigation is extended to cover a variety of configurations in terms of the radius of curvature
Dynamic response of doubly curved honeycomb sandwich panels to random acoustic excitation. Part 1: Experimental study
No full textA set of four doubly curved, composite honeycomb sandwich panels has been tested with broad band, random acoustic excitation in a progressive wave tube facility. This paper presents the experimental results in the form of dynamic face plate strain measurements taken from various points close to the centre of the panels, on both the inner and outer face plates. The panels were tested at overall sound pressure levels up to 164 dB (ref. 2×10?5 Pa, over a frequency bandwidth of 60–600 Hz). The response was found to be linear, with a maximum measured root mean square strain of 250?. The doubly curved geometry was found to have a profound effect on the ratio of inner-to-outer face plate strain, which was compared with ratios reported for flat and singly curved geometries. The second part of this study concentrates on three methods for predicting the response of the doubly curved panels to random acoustic excitation
LeTourneau modified tank-tree crusher with R.G. LeTourneau and unidentified man.
No full textPhotograph of a Tree Crusher Tender built in Vicksburg, Mississippi and intended for use at the Tournata complex in Liberia, according to author Eric Orlemann. Shown with the tank are R.G. LeTourneau, left, and an unidentified man. The tank was never actually shipped to Tournata
White Charolais cows brought to Peru by LeTourneau, Lt8 15159
No full textPhotograph of white Charolais cows brought to Tournavista, Peru by R.G. LeTourneau, Inc. The LeTourneau foundation established a mission site at Tournavista and cleared land in order for the occupants to raise cattle and crops
The effects of large vibration amplitudes on the mode shapes and natural frequencies of thin elastic shells, part I: coupled transverse-circumferential mode shapes of isotropic circular cylindrical shells of infinite length
No full textThe effects of large vibration amplitudes on the first and second coupled radial-circumferential mode shapes of isotropic circular cylindrical shells of infinite length are examined. A theoretical model based on Hamilton's principle and spectral analysis developed previously for clamped–clamped beams and fully clamped rectangular plates is extended to shell type structures, reducing the large-amplitude free vibration problem to the solution of a set of non-linear algebraic equations. The transverse and circumferential displacements are assumed to be harmonic and expanded in the form of a finite series of functions. The Donnel–Mushtarie shell theory, taking into account the coupling between extensional and flexural deformations is used. Then, the non-linear deformation energy is expressed by taking into account the non-linear term due to the considerable stretching of the middle surface of the shell induced by large deflections. Tables of numerical results are given for the first and second non-linear modes, for a wide range of the vibration amplitude, which may be used for engineering purposes. For each value of the vibration amplitude considered, the corresponding contributions of the basic functions defining the non-linear transverse and circumferential displacement shapes are given, with the corresponding non-linear frequencies. Selected plots of mode shapes and bending stress distributions are presented, with an extensive discussion of the effects of non-linearity on the dynamic behaviour of shells
On predicting the response of acoustically-excited doubly curved sandwich panels
No full textThis paper presents a recent programme of research, which has concentrated on the measurement and prediction of the dynamic response of doubly curved composite honeycomb sandwich panels to high intensity, random acoustic excitation. Four panels with varying radii of curvature were tested in a progressive wave tube (PWT) facility at overall sound pressure levels up to 164 dB (re 2×10?5 Pa). Several methods are presented to predict the dynamic response of the panels to random acoustic excitation. The first of these was the single-degree-of freedom (SDOF) approximation method, where different assumptions with regard to the spatial characteristics of the pressure loading are made. Finite element analysis (FEA) was also used to predict the response, where the pressure loading was assumed to consist of a series of travelling waves at grazing incidence to the structure.
The results presented for both the SDOF approximation method and the FEA method show good agreement between predicted and measured strain values, which are also presented
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