Dynamics of deep water moorings
Mechanics of Impact
Vehicle Dynamics and Road Damage
Vibration of Uncertain Structures
Probabilistic and Possibilistic Methods
Statistical Energy Analysis
Vibration of Complex Structures
Mechanics of Musical Instruments
Vibration Damping Modelling
Transmission of Vibrations from Railways into Buildings
Fault Identification using Neural Networks
Institute of Physics Award
Wavelet and Time-Frequency Analysis
Professor R.S. Langley
Future oil production may occur in water depths in excess of 2000m. This project is investigating the statics and dynamics of deep water mooring lines made of fibrous materials. Both geometric and material non-linearities are of particular concern. This project is funded by BP-Amoco.
Professor Langley has been elected Fellow of the Acoustical Society of America. The citation is for "contributions to understanding complex vibratory systems".
Dr W.J. Stronge
Fundamental research is continuing into deformation processes during impact with the aim of obtaining a physical basis for parameters representing low speed or "rigid body" impact where deformations are small. This research is relevant to constraints on operation of mechanical linkages in high speed assembly operations, impact printers and sports mechanics. A EUROMECH conference (Mechanical Impact in Multibody Systems) was organised this year to promote discussion of the various methods for analysing impact on multibody systems. For mechanisms consisting of stiff bodies with compliant contacts the spread of impact effects throughout the mechanism has been shown to progress as a dispersive wave, with interactions depending on the gradient of relative compliance. In oblique collisions between hard bodies that are rough (i.e. where friction is not negligible) the energy absorbed during collision can be separated into part due to friction and part due to plastic deformation and elastic waves. At low impact speeds these separate parts are decoupled.
Work continues on obtaining methods of assessing risk of perforation in metal structures subjected to impact by small sub-ordnance velocity fragments or missiles. Failure criteria representing kinematic constraints on deformation as well as material properties are being developed for oblique penetration and dishing of thin to moderately thick metal plates.
Dr D. Cebon
A comprehensive hand-book on vehicle-road interaction was completed. It discusses tyre-road contact forces generated by heavy vehicles: their influence on road surface and bridge response and damage; as well as ways of regulating and improving vehicles so as to minimise road damage (Handbook of Vehicle-Road Interactions)(F8).
Research continued on use of advanced suspension technologies to improve heavy vehicle safety, particularly roll-over, and reduce road damage. A comprehensive theoretical and experimental investigation of the rolling resistance of lorry tyres is currently underway. A new method for assessing the fatigue life of vehicle components has been developed. Considerable support in cash and kind has been received from the industrial members of the Cambridge Vehicle Dynamics Consortium (Tinsley Bridge Limited, Meritor HVS, Koni BV, Dunlop Tyres, Volvo Trucks, DERA, Shell, General Trailers, and Fluid Power Design). This work is co-funded by two EPSRC grants.
An EC-funded project on the use of multiple-sensor `weigh-in-motion' systems for measuring the weights of heavy vehicles travelling at high speeds, is nearing completion(F9). A programme of experimental measurements was undertaken on the A34 trunk road in Oxfordshire, using an array of 20 wheel force sensors embedded in the road surface(F29). The results have been used to verify predictions of theoretical models.
Dr J.D. Smith
A book on gear noise and vibration has been published(F27) and industry has been helped on gearbox reliability and life problems, especially in relation to rolling bearings. Further work on modelling non-linear vibrations with gears which have errors and misalignments has resulted in simplified computation methods(F28). Practical comparisons have shown the effectiveness of Smith Shock techniques for monitoring scuffing in critical situations.
Work on low frequency vibration measurement, originally for railway line measurements, is being extended to allow portable measurement of very low frequency structural vibrations. A method for recording slip in disc testing machines to better than 1 part in 105 has been devised and made.
Professor R.S. Langley
At medium to high frequencies the vibration response of a structure can become extremely sensitive to small changes in the system properties. Recent work has investigated a random point process model of the natural frequencies of an uncertain system, and this has highlighted the severe limitations of the commonly employed Poisson model. Further work is being performed in the area of natural frequency statistics and random matrix theory.
Professor R.S. Langley
Uncertainty is normally modelled in statistical terms, although in many practical situations (for example the automobile and aerospace industries) the poor quality and quantity of the available input data does not justify a complex probabilistic analysis of the system. Recently a number of possibilistic methods have been developed, including interval analysis, convex set theory, and fuzzy set theory. Current work is directed at providing a unified computational framework for probabilistic and possibilistic methods, so that the same code can be used to perform each of the methods. With this approach the method employed can readily be matched to the level of available knowledge regarding the input parameters. This work is in collaboration with DERA Farnborough.
Professor R.S. Langley
Work has been directed at providing a hybrid dynamic analysis procedure that couples statistical energy analysis (SEA) and the finite element method. With this approach the long wavelength deformation of the structure is modelled deterministically using finite elements, while the short wavelength motion is modelled statistically using SEA. This addresses the complex dynamics that can occur in an automobile or marine structure at medium frequencies. This work is funded by Vibro-Acoustic Sciences via the RESOUND consortium.
Dr J. Woodhouse
In a complex structure at medium and high frequencies, deterministic modelling of vibration must give way to a statistical description of some kind. In the particular context of long cylindrical structures such as a submarine pressure hull, the standard statistical methods give rather poor predictions. A new model based on one-dimensional power flow in coupled subsystems has been developed to address the problem(F4,F5). This new model allows for imperfections in the cylinder geometry, which have the effect of coupling different waveguide modes of the idealised structure. Such coupling can lead to "short-circuiting" of measures added to the structure to impede vibration transmission, and is the main reason for the poor performance of the earlier models. The new model allows much more realistic estimates to be made of the performance of a proposed vibration-control measure.
Dr J. Woodhouse
The vibrational behaviour of musical instruments continues to provide challenging scientific problems. An extensive study was reported last year into the effect on the motion of a bowed string of the finite width of the ribbon of bow hair. The final part of this has now appeared in print(F26). In another area of violin acoustics, a beneficial effect has been reported by many violin makers when the vibration frequencies of two different modes of the structure are tuned into close proximity.
A theoretical and experimental study has been carried out of the acoustical consequences of such matching(F33). This has allowed the matching process to be carried out more easily, and also suggests experiments which might be made to pin down the precise limits on any benefits which accrue.
Dr J. Woodhouse
The theory of structural vibration is highly developed in the representation of the effects of mass and stiffness, but the modelling of damping is much more primitive and controversial. In a recent development(F31), it has been shown that provided damping is linear and light, then the effect of very general damping forces can be incorporated very straightforwardly into the standard undamped theory. This allows very general damping to be added into, for example, Finite-Element calculations by post-processing. It has also opened the way to new studies of the extent to which the characteristics of damping in a real structure can be established by measurement.
Dr H.E.M. Hunt
Professor D.E. Newland
Vibration transmission from railways into buildings is being analysed from the perspective of power flow. New performance indicators are proving far more illuminating than the conventional "Insertion Loss". New materials are being developed for the measurement and control of vibrational power flow. The use of power-flow transducers in buildings permits accurate validation of analytical models. These include models of tunnels and buildings based on repeating-element theory(F10,F11).
Dr H.E.M. Hunt
Fault identification in structures using vibration data makes use of neural networks using the maximum-likelihood method and a Bayesian approach. Modal energies calculated from frequency-response functions give rise to new assurance criteria which are used in conjunction with more conventional criteria based on modal properties. A committee of neural networks gives lower mean-square error and therefore better classification of faults than the individual methods.
The 1999 Public Awareness of Physics Award was awarded to Dr Hunt, jointly with Dr Mark Warner of the Cavendish Laboratory, for their public lecture "Spinning into Space" which was given during the National Week for Science, Engineering and Technology in March. The citation recognises their success in presenting difficult concepts in an accessible and entertaining way to a widely mixed audience.
Professor D.E. Newland
The harmonic wavelet method of time-frequency analysis has been developed for application to multi-channel data, and time-varying cross-spectra can be computed efficiently by this approach. Cross-spectral data, both amplitude and phase, is presented in the form of coloured two-dimensional maps. Applications studied to date include the transmission of ground vibration caused by underground railways and measurement of the nonlinear behaviour of soil specimens under earthquake loading in laboratory tests(F21,F22,F23,F24,F25).
F1. Aglietti, G.S., Langley, R.S., Rogers, E. Monte-Carlo studies of control system robustness for an equipment loaded satellite panel. 4th International Conference on the Dynamics and Control of Structures in Space, Cranfield, Bedfordshire (May 1999).
F2. Bardell, N.S., Dunsdon, J.M., Langley, R.S. Free vibration of thin, isotropic, open, conical panels. Journal of Sound and Vibration, 217, (2), 297-320 (1998).
F3. Bardell, N.S., Langley, R.S., Dunsdon, J.M., Aglietti, G.S. An h-p finite element vibration analysis of open conical sandwich panels and conical sandwich frusta. Journal of Sound and Vibration, 226, (2), 345-377 (1999).
F4. Blakemore, M., Woodhouse, J. Power-flow analysis of quasi-one-dimensional systems with distributed coupling. Proceedings, IUTAM Symposium on Statistical Energy Analysis, Southampton (July 1997); Edited by F.J. Fahy, W.G. Price, 163-174 (Kluwer, Dordrecht, 1999).
F5. Blakemore, M., Woodhouse, J., Hardie, D.J.W. Statistical power-flow analysis of an imperfect ribbed cylinder. Journal of Sound and Vibration, 222, (5), 813-832 (1999).
F6. Browne, M., Langley, R.S., Gregson, P.J. Reliability theory for load bearing biomedical implants. Biomaterials, 20, (14), 1285-1292 (1999).
F7. Browne, M., Langley, R.S., Gregson, P.J., Walker, P.S. Reliability theory for the knee tibial tray. 15th European Conference on Biomaterials, Arcachon, France (September 1999).
F8. Cebon, D. Handbook of Vehicle-Road Interaction. (Swets and Zeitlinger B.V., Lisse, the Netherlands, 1999). ISBN 9026515545
F9. Cebon, D. Multiple-sensor WIM systems. Weigh-in-Motion of Road Vehicles: Proceedings, Final Symposium of the Project WAVE (1996-1999), Paris, France (May 1999); Edited by B. Jacob (Hermes Science Publications, 1999). ISBN 2-7462-0050-3.
F10. Forrest, J.A., Hunt, H.E.M. Ground vibration due to trains in underground railway tunnels. Proceedings, 6th International Congress on Sound and Vibration, Lyngby, Copenhagen, Denmark (July 1999).
F11. Hunt, H.E.M. The effectiveness of floating-slab track for railways in tunnels. London Authorities Rail Impact Forum, Conference on the Vibration Effects of Railways and Other Guided Means of Transport, Bromley, Kent (September 1999).
F12. Khumbah, F.M., Langley, R.S. Efficient dynamic modelling of aerospace box-type structures. Internoise 98, 1998 International Congress on Noise Control Engineering, Christchurch, New Zealand (November 1998).
F13. Langley, R.S. An introduction to statistical energy analysis. ESDU (Engineering Sciences Data Unit) Data Item 99009 (ESDU International, 1999).
F14. Langley, R.S. A non-Poisson model for the vibration analysis of incertain dynamic sustems. Proceedings of the Royal Society of London Series A: Mathematical, Physical and Engineering Sciences, A455, (1989), 3325-3349 (1999).
F15. Langley, R.S., Bremner, P.G. A hybrid method for the vibration analysis of complex structural-acoustic systems. Journal of the Acoustical Society of America, 105, (3), 1657-1671 (March 1999).
F16. Lim, C.T., Stronge, W.J. Oblique elastic-plastic impact between rough cylinders in plane strain. International Journal of Engineering Science, 37, (1), 97-122 (1999).
F17. Liu, D., Stronge, W.J. Ballistic limit of rigid-plastic plates struck by deformable missiles. Impact Engineering Conference, Singapore (November 1998).
F18. Marwala, T., Hunt, H.E.M. Fault identification using a committee of neural networks. Proceedings, 2nd International Conference on Identification in Engineering Systems, Swansea, 102-111 (March 1999).
F19. Marwala, T., Hunt, H.E.M. Fault identification using finite element models and neural networks. Mechanical Systems and Signal Processing, 13, (3), 475-490 (1999).
F20. Nair, P.B., Keane, A.J., Langley, R.S. Improved first-order approximation of eigenvalues and eigenvectors: reply by the authors to R.A.Canfield. AIAA Journal, 37, (7), 900-901 (1999).
F21. Newland, D.E. Harmonic wavelets in vibrations and acoustics. Proceedings, Royal Society Discussion Meeting, Wavelets: the key to intermittent information?, London (February 1999). Published in: Philosophical Transactions of the Royal Society of London Series A: Mathematical, Physical and Engineering Sciences, A357, (1760), 2607-2625 (September 1999).
F22. Newland, D.E. Ridge and phase identification in the frequency analysis of transient signals by harmonic wavelets. Transactions of the ASME, Journal of Vibration and Acoustics, 121, (2), 149-155 (1999).
F23. Newland, D.E., Butler, G.D. Application of time-frequency analysis to strong motion data with damage. 69th Shock and Vibration Symposium, US Government's Shock and Vibration Information Analysis Center (SAVIAC), Minneapolis/St. Paul, MN, USA (October 1998) (1998).
F24. Newland, D.E., Butler, G.D. Time-frequency analysis of transient vibration data from earthquake centrifuge testing. Proceedings, 6th International Congress on Sound and Vibration, Lyngby, Coppenhagen, Denmark, 4, 1879-1886 (July 1999). ISBN 87-987457-9-4.
F25. Newland, D.E., Butler, G.D. Time-varying cross-spectra by harmonic wavelets for soil motion with damage. Proceedings, 1999 ASME Design Engineering Technical Conferences, 17th ASME Biennial Conference on Mechanical Vibration and Noise, Las Vegas, NV, USA, 726 (September 1999). ISBN 079181967-1.
F26. Pitteroff, R., Woodhouse, J. Mechanics of the contact area between a violin bow and a string. Part III: parameter dependence. Acustica/ Acta Acustica, 84, (5), 929-946 (1998).
F27. Smith. J.D. Gear Noise and Vibration. (Marcel Dekker, Inc, New York, 1999). ISBN 0824760050.
F28. Smith, J.D. Modelling the dynamics of misaligned helical gears with loss of contact. Proceedings of the Institution of Mechanical Engineers, Part C, Journal of Mechanical Engineering Science, 212, (C3), 217-224 (1998).
F29. Stergioulas, L.K., Cebon, D. An experimental trial of multiple-sensor weigh-in-motion. Cambridge University Department Technical Report CUED/C-MECH/TR.79 (1999).
F30. Woodhouse, J. The acoustics of "A0-B0 mode matching" in the violin. Acustica/Acta Acustica, 84, (5), 947-956 (1998).
F31. Woodhouse, J. Linear damping models for structural vibration. Journal of Sound and Vibration, 215, (3), 547-569 (1998).
[Table of Contents]
Last modified: July 2000