General engineering analysis

Case Study

Innovative dynamometer design

Design & Projects Limited provides an engineering design and project management service that specialises in providing solutions to novel and complex engineering challenges. Typical of the type of work routinely undertaken with the aid of LUSAS Analyst is an innovative design for a new type of dynamometer - intended for use in testing aircraft tyres and brakes in the USA.

With conventional dynamometers, test wheels run on the outside of the roadwheel. However, in this design brief, it was proposed to run the test wheel inside the roadwheel flange, with the benefit of allowing surfacing to be applied to the inside of the flange to give a more realistic testing arrangement. Test wheel tyre sizes of 18-56" diameter and having widths varying between 6-25" had to be accommodated. Recommended design ratios for test and roadwheel diameters resulted in a dynamometer internal flange diameter of 172" being required to give the correct amount of tyre contact. Tyre loads of 150,000 lbf acting vertically and 30,000 lbf acting normal to the wheel's plane of rotation had to be applied to the LUSAS model and a roadwheel speed of 350 mph was to be used to arrive at maximum in-service stresses. Because of the type of analysis required, the use of LUSAS was considered essential in order to achieve a credible and cost-effective solution

From initial studies, hoop stresses in the flange were found to exceed 400MPa. Since centrifugal stresses accounted for the majority, there was little scope for refining a conventional design so this led to the development of a scheme to add a shrunken rim to the flange of the roadwheel, to induce compressive stresses in the stationary state. The profile of this rim allowed material of a higher strength than the roadwheel to be used.

Stresses from fitting shrunken rim

Stresses from tyre loading and 350 mph roadwheel speed

Stresses from fitting shrunken rim Stresses from tyre loading and 350 mph roadwheel speed

LUSAS was used to investigate the effects of varying the relative thicknesses of the flange and rim, together with looking at changes in the interference fit. As the roadwheel was basically asymmetric, the Fourier analysis capability of LUSAS was used. This allowed small changes to be incorporated and re-analysed rapidly. The effectiveness of this approach was tested against a simpler model analysed both symmetrically and as a full 3D model. An optimum loading pattern was found to simulate tyre landing impact and used throughout the remaining study. The innovative dynamometer design was judged a success with a good balance being achieved between the initial compressive stresses and the maximum operational tensile stresses. From the results obtained an additional fatigue assessment was done to evaluate any potential fatigue problems.

"This project is typical of the work we undertake. We specialise in undertaking novel engineering challenges so we need analysis software that provides reliable answers for any type of analysis problem. LUSAS Analyst meets our needs in this respect and helps to enhance our in-house design skills in a very cost-effective way".

Bill Coleman, Director at Design & Projects


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