Development of a force/moment-measurement system for Static and Dynamic Testing of underwater Models in a Water Tunnel

The measurement of hydrodynamic forces on underwater bodies is one of the principal uses for water tunnels. This paper describes the design of a new six-component force-moment strain gauge balance system with bending beams for measuring forces Fx, Fy and Fz and moments Mx, My and Mz in water tunnel models. A balance team at the Applied Hydrodynamics Laboratory of IUST performed many areas for designing balance system such as structural design, balance technology, balance calibration, designing sting mount system, etc. The concept used in the balance design is the bending beam and strain gauge principle. In the structural design of the balance the dimensions of the "optimum" section and the likely deflection of the balance under load were determined using finite-element analysis. The material of balance was selected based on stress level and on the available space. Also, The material selection have a strong influence on the hysteresis, creep and repeatability characteristics of the force balance. Production technology of the balance have been developed based on the design concepts, materials, different balances, process of new material and construction techniques. Details of the calibration methodology and the equipment constructed are given in this paper together with the sensitivity matrix. This balance is located inside water tunnel and connects the model structure to the mounting sting. The sting mount has been designed for the static and dynamical tests.