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Feature 1 | DANISH MARINE INDUSTRIES DPLab from dynamic Force


Force Technology is applying its DPLab dynamic positioning ‘holding capability’ soſtware to an ever broader range of vessel types.


According to Thomas Eefsen, senior project manager at Force Technology’s Hydro and Aerodynamics laboratory in Denmark, these projects cover the range, from numerical predictions to full blown model tests on ships and semi-submersibles. “In a project regarding dynamic


F


positioning, the following three questions need an answer: is station keeping possible under current conditions? What size of thrusters is required and where do we need to install them to maximise their effect? And how are the thrusters best utilised? Mr Eefsen notes that these three


problems do not, of course, have independent solutions. “A common solution solving all three must be found.” For this purpose, Force Technology has developed the Holding Capability Module for its DPLab soſtware, intended for in-house use or as soſtware sold in a


orce Technology has been involved in numerous dynamic positioning (DP) projects since the early 1990s.


DPLab provides access to database of wind and current loads.


package with wind and current predictions or wind tunnel model tests. Te program follows the recommendations of the International Marine Contractors Association.


The data display allows for various analysis, database search or individual definition of thrusters and their efficiency.


The Basics version performs static


calculations, balancing the available thrust with environmental forces. The holding capability is defined as limiting environmental forces arising from wind, current and waves, that can be balanced by the vessel using its propulsive systems in an optimal way. Once the key data for the vessel or platform


has been assembled and entered into the program, various analyses can be performed. Tese include Failure Mode Analysis (FMA). It is important for any operator of a vessel featuring DP capability to be able to evaluate the ability to stay at position in case of failure on one or more units. Tis task is built into the soſtware of DPLab and is carried out, providing the client with rapid evaluation of the failures and their effects on the DP capability Te basic input data required for DPLab


are vessel geometry, wind and current force coefficients, second order wave driſt forces, thruster sizes and positions, and thruster efficiencies, that is, thruster to thruster interaction and thruster to hull interaction. Wind and current data are either obtained from predictions based on existing databases combined with Force’s empirical data, or alternatively from wind tunnel tests on the


30 The Naval Architect April 2009


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