IgH decided to use Model-Based Design. Using Simulink, they built a precise mathematical model of the entire salvage system. They could then evaluate options and predict system performance before testing their designs in real time.
The model included equations of movement for the barge and the Kursk, each in six degrees of freedom to account for the hydrodynamic forces generated by waves; a thermodynamic model of the gas pressure system; a mechanical model of the compensators and the hoists; a complete programmable logic controller (PLC) model, including connected sensors and actuators; and an interface to the computers controlling the PLCs. The cable lengths and the signals from two angle-of-tilt sensors were also modeled.
The model had to account for the position of the heave compensators with respect to the lifting cables and the weights to which each cable would be subjected.
Determining the Parameters
Since the control parameters for the heave compensators were the gas pressure and the stiffness of the gas springs, one major objective of the simulation was to determine these parameters in light of the environmental conditions.
Parameters for the different simulation scenarios were selected through a graphical user interface developed in MATLAB.
The simulation model also provided an interface to the control computers, which contained automatic valves to regulate pressure in the gas cylinders, length sensors mounted on the anchor cables, and other components that controlled the lifting mechanism. Thus, the control computers could be operated alternatively with the simulator to test their functionality.
IgH made full use of the open Simulink environment and the ability to integrate C code into the Simulink model. As Dr. Wilhelm Hagemeister, managing director of IgH, comments, "Most software packages for developing technical systems lack certain functions. That means that you have to program the whole solution yourself. In contrast, MATLAB and Simulink provide most of the functions required, and any other problems can be resolved by in-house development in MATLAB or by integrating our own source code."
IgH also used Simulink to develop control software for pressure regulation. This software could automatically calculate the optimum load distribution over the 26 lifting cables and adjust the gas energy in the heave compensators. It could be run with the Simulink model or directly with the PLC and could be fully tested before being used in action.
An Expanding Role for IgH
By using Model-Based Design, IgH gained an exceptional understanding of the system as a whole. As a result, their role expanded from consultant on one specific technical issue to "scientific lead" for the entire project.
As the company's responsibilities broadened, it became clear that all their new tasks could be accomplished using MATLAB and Simulink.
Shortly before the operation began, Russian experts compared results obtained from their own calculations and physical trials using a modeled submarine with those achieved by the IgH simulation. Based on these extremely close results, the raising of the Kursk could begin and a tragic episode in naval history be brought to a close.