TRIDISMA

PROJECT: MAS3-CT95-0017

Three-Dimensional Sediment Transport Measurements by Acoustics (TRIDISMA)

BRIEF DESCRIPTION OF THE RESEARCH PROJECT

 

The study of sediment transport is receiving growing attention as the demands placed on the coastal zone increase.. Unfortunately, however, sediment transport in the marine environment is notoriously difficult to measure, yet it's quantification is fun damental to numerous practical applications, from assessing the stability of dredge spoil sites and harbour siltation, to understanding the morphodynamics associated with beach erosion and coastal protection.

With this in mind the TRIDISMA project was established with funding from the European Commission's 3rd Marine Science and Technology Program ( MAST III ) to pursue investigations into the applic ation of non-intrusive acoustic methods into the measurement of sediment resuspension processes.

The primary objective of TRIDISMA has been to develop and test a prototype acoustic instrument to measure sediment transport profiles in the bottom 1-2 m above the bed by simultaneously measuring profiles of the suspended sediment concentration, partic le size and the three components of the fluid velocity. The range and variety of flow and sediment concentration and size conditions which the new instrument will encounter will has been defined and the Coherent Doppler and Correlation techniques extended to encompass these flow regimes. Experimental studies have been undertaken with the aim of improving our understanding of the interaction of sound with suspensions of sediments in water, particularly with respect to (i) the variation of the backscatterin g form function with sediment size and shape, (ii) the attenuation of acoustic energy due to the presence of sediment in the water and (iii) the effects of multiple-scattering at high sediment concentrations. Laboratory and theoretical studies into the in teractions between sound and suspensions of sediments have also been conducted. The problem of multiple scattering and the effects of scatterer shape on the far field backscattering form function has also been investigated using both numerical models and laboratory measurements.

A program of trials of the prototype instrument was commenced in September 1997 in a laboratory wave tunnel and data is presently being evaluated whilst a fie ld deployment in conjunction with other flow measurement and sediment measuring equipment was undertaken in March 1998 at Sea Palling on the UK's North Norfolk Coast.

The hardware that has been developed during the project was constructed to collect the very high density data sets required in the research phase of the instrument development. Subsequent commercial exploitation is expected to use significant on-board signal processing, however, the extent and appropriateness of such processing will not be known until the TRIDISMA been has been completed). Studies have also be conducted into the transducer design to produce the appropriate beam shapes for (i) the flow measurement and (ii) for the sediment concentration and particle size.

TRIDISMA has drawn together European partners with wide and extensive experience in the design, construction and use of high-frequency acoustic backscatter instrumentation for measuring suspended sediment concentrations in the marine environment. The p artners come from Industrial, Research and Academic areas, indicating the wide appeal of this project. A number of partners in TRIDISMA have used acoustic instruments to make coastal, beach and estuary measurements of suspended sediment concentration or o f velocity, some of which were conducted under previous EU programmes. The industrial partners have an existing presence in the marine acoustic market and view this prototype intrument development as leading to new products helping to maintain the competi tiveness of European Industry in marine ultrasonics.

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COORDINATORS :

Dr Chris Vincent

Dr Jonathan Taylor

University of East Anglia School of Environmental Sciences,
Norwich NR4 7TJ, U.K.
Tel. : +44 1603 59 25 29
Fax : +44 1603 50 77 19
e-mail : c.vincent@uea.ac.uk

OTHER PARTNERS

Delft Hydraulics
PO BOX 177,
2600 MH Delft,
Holland.
Tel. : +31 15 58 9353
Fax : +31 15 61 9674
e-mail : arjen.schaafsma@wldelft.nl
Principle Investigator Dr Arjen Schaafsma

Proudman Oceanographic Laboratories
Bidston Observatory, Birkenhead,
Merseyside L43 7RA, U.K.
Tel. : +44 151 653 8633
Fax : +44 151 653 6269
e-mail : pdt@unixa.nerc-bidston.ac.uk
Principle Investigator Dr Peter Thorne,

Thompson Marconi Sonar

Route de Ste-Anne du Portzic
29601 Brest Cedex, France
Tel. : +33 98 31 3928
Fax : +33 98 31 3975
Principle Investigator Mr Marc Perennes

University of Bath
School of Physics
Claverton Down
Bath BA2 7AY
Tel. : +44 1225 826 826
Fax : +44 1225 826 110
e-mail : v.f.humphrey@bath.ac.uk
Principle Investigator Dr Victor Humphrey

TechSonic
Les Alisiers, Route des Alisiers
Z.I. Les Trois Moulins
06600 Antibes, France
Tel. : +33 93 74 68 58
Fax : +33 93 74 33 14
Principle Investigator Dr Daniel Guyomar

Technical University of Denmark
Dept of Industrial Acoustics
Building 425
2800 Lyngby, Denmark
Tel. : +45 45 25 4766
Fax : +45 45 93 0190
Principle Investigator Prof Leif Bjorno

 

Papers produced during TRIDISMA

I.K. Bjørnø, L Bjørnø Modelling of multiple scattering in suspensions, Proceedings of 3rd European Conference on Underwater Acoustics, Crete, Greece 24th-28th June 1996 pp87-92

L Bjørnø and I Bjørnø Acoustical scattering from suspensions of sand and gas bubbles close to the sea bed. 4th French Congress on Acoustics, Marseilles 14th-18th April 1997 Vol. 2 1085-1088

S Shaobo, D Li and IK Bjørnø Theory and measurements on scattering by two spheres, Technical Report IA-TR-64 1997 34pp.

J Hald Evaluation, definition, construction and tank tests on acoustic transducers, Technical Report IA-TR-62 1997 43pp

Chinnery, P.A., Humphrey, V.F. and Zhang, J.D. (1997). "Low-frequency acoustic scattering by a cube: Experimental measurements and theoretical prediction". Journal of the Acoustical Society of America, 101 (5), 2571-2582.

Chinnery, P.A., Humphrey, V.F. and Zhang, J.D. (1997). "Acoustic scattering by non-metallic and metallic cubes in the elastic resonance regime: Experimental measurements and combined finite / boundary element modeling". Journal of the Acoustical Society of America, 102 (1), 60-66.

Humphrey, V.F., Zhang, J.D. and Chinnery, P.A. (1998). "Experimental Measurements and Theoretical Modelling of Acoustic Scattering by a Cube." Proceedings of the 16th International Congress on Acoustics and 135th Meeting of the Acoustical Society of America, 505-506.

Zhang, J.D. and Humphrey, V.F. (1998). "Numerical modelling and experimental measurement of the acoustic scattering by two elastic spheres". Proceedings of the 4th European Conference on Underwater Acoustics, (in press).

Schaafsma A.S., and Hay A.E. Attenuation in suspensions of irregularly shaped sediment particles: a 2-parameter scattering model. Submitted to J Acoust. Soc. Am

Schaafsma A.S., Lafort A.M. , Mazoyer T and Guyomar D Attenuation spectroscopy to characterise sediment Part I theoretical and experimental validation of attenuation spectroscopy. Submitted to Acta Acustica.

Schaafsma A.S., and Thorne P.D. Local profiling methods for acoustic measurements of suspended sediments Oral Presentation at 4th European Conference on Underwater Acoustics, Rome. September 1998

Bell P.S., Thorne P.D. and Williams J.J Acoustic measurements of sand ripple profile evolution under controlled wave conditions. Oral Presentation at 4th European Conference on Underwater Acoustics, Rome. September 1998.

Thorne P.D and Hardcastle P.J. Measurement of nearbed current profiles using coherent Doppler and cross correlation techniques. Oral Presentation at 4th European Conference on Underwater Acoustics, Rome. September 1998.

Thorne P.D., Hardcastle P.J. Taylor J.A. Humphrey V.F, Zhang J.D. Schaafsma A.S and Janssen M. Utilisation of multi-frequency acoustics for studying suspended sediment processes: Assessment and results under currents waves and combined currents and waves. Oral Presentation at 3rd European Marine Science and Technology Conference Lisbon. May 1998

J A Taylor, C E Vincent, P D Thorne, P J Hardcastle, V F Humphrey, J D Zhang, A Schaafsma, A Lafort and M Perennes Three-Dimensional Sediment Transport Measurements By Acoustics (TRIDISMA). Oral Presentation at Oceans 98 Nice September 1998

V F Humphrey J Zhang and P.A. Chinnery Experimental measurements and theoretical modelling. of acoustic scattering by a cube Submitted for Oral Presentation at 16th International Congress on Acoustics and 135th Meeting of the Acoustical Society of America June 1998