Design and fabrication of a force-moment measurement system for testing of the models in a water tunnel

The measurement of hydrodynamic loads on submerged bodies is one of the principal uses of water tunnels. Due to the limitations of the water tunnel, an accurate force balance is necessary. This paper describes the design, fabrication and calibration of a new six-component force moment balance system for measuring the forces and moments acting on the model, in static and dynamic water tunnel testing. A balanced team performed many areas for designing balance system such as structural design, balance technology, design of calibration mechanism, balance calibration etc. A six-component balance, ability to measure the three elements of force and three components of moment simultaneously and instantly on cavitating and non- cavitating models in a water tunnel. The concept used in the balance design is the bending beam and the strain gage principle. The electrical signals are proportional to the forces applied to the model. By considering the relationship between the applied force and the balance’s output signal and by using the calibration models, the forces and moments exerted on the model in the water tunnel can measure directly. For calibrate multi component balance, a new six-degree of freedom calibration rig designed and constructed. The system is designed based on applicability of formal experimental design techniques, using gravity for balance loading and balance position and alignment relative to gravity. The six-component balance was calibrated by this rig. The standard error between the measured values and the values obtained from calibration model is less than 0.1 percent of maximum loading was achieved.