ABSTRACT
Introduction Horizontal platform devices are widely used in offshore engineering and earthquake engineering. Mechanical model for a horizontal platform system with an accelerometer is depicted in Fig. 1. The platform can freely rotate about the horizontal axis, which penetrates its mass center. When the platform deviates from horizon, the accelerometer will give an output signal to the torque generator, which generates a torque to inverse the rotation of the platform about rotational axis. The equation governing this system is
3sin ( )cos sin cosgAy Dy rg y B C y y F t R
ω+ + − − = ,
where y denotes the rotation of the platform relative to the earth, BA, and C are respectively the inertia moment of the platform for axis 1, 2, and 3, D is the damping coeffi cient, r the proportional constant of the accelerometer, g the acceleration constant of gravity, R the radius of the earth and tF ωcos harmonic torque. More details about this model can be found in Refs.[1,2]. Such horizontal platform systems can reduce the swing of moving devices and keep the system close to horizontal position. They are used in modelling offshore platforms and earthquake-proof devices.
