Design of Six-Component Force/Moment Sensor For Cavitation Tunnel

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Abstract

The measurement of hydrodynamic forces on underwater bodies is one of the principal uses for water tunnels. For this type of work an accurate force balance is necessary. This paper describes the design of a new six-component force-moment strain gauge balance with bending beams for measuring forces and moments simultaneously and directly on cavitating and Non-cavitating models in water tunnel. This balance is a complex structural spring element, which provides high-precision measurements of the hydrodynamic loads exerted on the water tunnel model, by measuring strain within its flexural elements. This measured strain is then converted into an electrical signal. Electrically measured strain as a function of an externally applied load forms. The main idea of the new balance design is to translate all desired forces and moments in such a way that they yield bending strain at selected strain-gauge station. This is done by using bending balance geometry. A strain gauge balance is a complicated structure with a very large number of dimensions. So the balance design cannot be achieved as an analytical solution from the external dimensions and the required component ranges. The dimensions of the "optimum" section and the likely deflection of the balance under load were determined using finite-element analysis. Hydrodynamic loads on typical water tunnel models were calculated, and the results were used to determine the strain level required to obtain the desired sensitivity. The size of the cantilever beams was carefully planned in order to determine the appropriate strain gauges needed for the experiment.

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References

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Journal of Solid and Fluid Mechanics
Volume 4, Issue 1 - Serial Number 1
March and April 2014
Pages 131-137

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