Ship Motion Monitoring And Short-term Forecasting

The ship in waves can produce six degrees of motion as well as any rigid body: heave, sway, surge, pitch, roll and yaw. With the development of the computer, it is the consensus that strapdown inertial navigation system (SINS) is a very effective way of rigid body motion measurement. It's commonly used in the missiles and other aircrafts, such as rockets, planes. It also has been used in large scale warships, especially ships with aircraft platforms, such as aircraft carriers and submarines. With the strapdown inertial navigation system becoming more and more increasingly popular in the civilian usage, and the demand of acquiring ship hull motion statement of Aircraft carriers and submarines, promoted the marine SINS development. It can be forcasted in the near future high-performance and low-cost strapdown inertial navigation systems will be used widely in the merchant ships.The measured data based on inertial navigation system can be used for short-term forecasting the ship's motion and providing security for planes taking-off and landing on aircraft carrier. On the other hand, this system can provide technical support for long-term underwater activity of the submarines. Since the SINS is a self-sustaining system, and don't need any information provided by outside world. So the submarine do not need to emerge from the underwater to do the GPS orientation from time to time, which improves submarine's hidden ability.The main contents of this paper are:1. The solve theory of non-gyro SINS has been studied. The expressions of accelerations of any point on the carriers in the inertial coordinate system have been deduced.2. The initial alignment requirement of the non-gyro inertial navigation marine platform has been discussed. How to choose the proper time to install the SINS and the notes needed to pay attention to are discussed.3. With reference to previous research data and the thorough study conducted on SINS, the SINS models composed by six accelerometers, nine accelerometers and twelve accelerometers have been discussed respectively. For different configuration of the accelerometers, the method to solute the angular velocities and linear velocities have been derived. The advantages and disadvantages between the models have been compared and analyzed. To solve the equations with the information get by the gyroscope which measures the angular velocity has been proposed and the effect is good. Finally, the correctness and the utility of the models have been verified through computer simulation.4. How the error is generated of the SINS has been analyzed. The impact on solution caused by installation error of the accelerometers has been simulated by computer. The effective and delicate error compensation method has been proposed.5. The methods of ship's short-term forecasting have been discussed. Since time-domain data can be derived by SINS, through the comparative study of the six methods, two methods fit the SINS have been summed up, ie, the cycle map method and time series analysis method. The modeling conception and means based on AR auto-regression method have been proposed. The methods mentioned in this article provide a reference for real ship's monitoring and forecasting in the future.