ON THE HOISTING AND LOWERING OF SUCTION PIPES A DYNAMIC MOTION ANALYSIS

摘要

With the introduction of jumbo trailing suction hopper dredgers and the development of deep sea dredging equipment came suction pipe constructions and gantries of ever increasing dimensions. The implementation of submerged dredge pumps and the application of longer and greater number of pipe sections of large diameter resulted in suction pipe constructions which distinguish themselves from traditional constructions by their bigger mass and deviating mass distribution. Given the fact that these characteristics have changed significantly and are features that determine the dynamic motion behaviour of a suction pipe construction, one enters a new field concerning the dynamic behaviour of these constructions. This paper describes a mathematical model, developed at IHC Holland's R&D institute MTI Holland in cooperation with Delft University of Technology. With this mathematical model one can perform calculations in the frequency domain to determine the eigenvalues and eigenvectors of an arbitrary suction pipe construction during the hoisting or lowering operation above the water line. These eigenvalues and eigenvectors determine the dynamic motion behaviour of the suction pipe construction. By implementing the motions of the vessel into the model it was furthermore made possible to determine the motion behaviour of suction pipe constructions while working in offshore conditions. The probability of the draghead and gimbal joint colliding with the hopper dredger's hull in a certain seastate can be calculated as well as the occurring collision speeds. This knowledge can be used to evaluate performance and operating limits of dredging equipment working in offshore conditions. With the mathematical model a tool is developed to analyse the dynamic behaviour of existing suction pipe constructions or suction pipes which are still in an early stage of the design phase.