Research On Liquid Cargo Handling Intelligent Control System Key Technologies

In order to improve handling efficiency of tankers,reduce the time of the ship settling in port and increase economic benefit,the liquid cargo handling system(LCHS) tends to complication and intelligence with the development of many subjects like computer, automatic control,signal process and shipping transport service,which is consist of many subsystems such as loading/unloading system,inert gas system,tank depth measurement system,high/high-level alarming system etc.How to integrate these subsystems which have time-delay or time-varying is difficult problem.The liquid cargo handling systems of high performance ships in out country depend on directly importing foreign advanced technology,which leads to some questions:(1) The foreign LCHS is a technology black box for us due to existing economic interests.(2) The tuning of parameters is very complex in foreign LCHS although it has advanced process control and optimization techniques.(3) there is a lack of self-developed engineering LCHS because of directly importing LCHS. So it is very important in theory and practice that research on the key technologies of LCHS.This paper is on the basis of the domestic and foreign research status of LCHS, further the research work in this domain.And the main contents are as follows:(1) Aiming at having the nonlinear and non-stationary property of signals in LCHS, we mainly studied the Empirical Mode Decomposition(EMD) algorithm which was suitable for nonlinear and non-stationary signal.In order to improve the precision of local-EMD, when to get the first Intrinsic Mode Function(IMF),we firstly adopted three points sliding average method to get the mean of data envelopment which did not distinguish extremum,then used the non-uniform B-spline curve to interpolate data.Other IMFs were gotten by using cubic spline to fit maximum envelope and minimum envelope respectively. The improved method could avoid the overshoot and undershoot in high-frequency decomposition of signal data.(2)One method was proposed to solve the mode mix problem.The signal data was retreated with wavelet transform,because pseudo-Gibbs caused by wavelet transform still brought mode mix problem,so we adopted the de-noising method based on translations invariant performed the cycle spinning for the signal to be analyzed at first.Secondly,the soft(hard) thresholding was used to de-noise the sfifted signal,then one should shift the data of the de-noised signal in reverse.At last,the treated signal data was decomposed by EMD.(3)Many mathematical models of subsystems of LCHS could not be suitably given, so it is difficult to control the subsystems by using modern control theory.We studied the model free control algorithm which is a new control algorithm and combines modern theories with classical PID,and then we proposed the model free control of pseudo gradient estimation algorithm based on multi-innovation theory and the model free control method of model free control law based on multi-innovation theory,which improved the convergence performance of model free control algorithm by making full use of the past input/output data.The theoretical derivation and convergence proof of two methods were given,which showed the proposed methods were efficient and effective.At last,we studied the parameters optimization of the two methods based on Particle Swarm Optimization (PSO) and Artificial Fish Swarm(AFS).(4)Faced to engineering practice,a framework of LCHS based on open control system structure was proposed,in which the designer can add new algorithms according to specific problems but not considering the hardware.A practical LCHS of 16000DWT tanker was constructed.Based on the implement system,we researched on the signal process of liquid level by using proposed local-MED algorithm in the paper and the control effect of the proposed multi-innovation model free control method in pressure and flow of liquid cabin.And we completed a real-time stowage system of 12000T floating dock and a real-time stowage system of 5000T semi-submersible barge,which could show that the proposed framework in the paper has engineering value.