The offshore support vessels (OSV) cover a variety of vessels from relatively simple Platform Support Vessels (PSV) to Anchor Handling Tug Supply (AHTS), Construction Vessels, Inspection, Maintenance and Repair (IMR) Vessels, Diving Support Vessels, Standby Vessels, etc.
Naturally, the design needs to be balanced for the vessel to be able to perform its tasks safely, but the general focus on environmental performance and fuel efficiency seen on commercial vessels has also reached the OSV industry. Therefore, the many different vessel types, the variation in the tasks they perform and the focus on energy efficiency increase the demand for optimal design in regard to their operational profiles.
FORCE Technology offers the full range of numerical and experimental services required by the builders and operators of OSV’s. These services include analyses of hull forms for powering requirements, analyses of manoeuvring and dynamic positioning, seakeeping analyses, wind tunnel tests, and simulations. In the following, we present some of the more important issues to consider in the design phase.
As for all vessels, the powering performance of an OSV is important. Designers and shipyards must ensure that the vessel can meet the contract specifications with a reasonable margin in terms of speed and power requirements. But at the same time, the owner must ensure that his vessel is optimised as far as possible to minimise fuel consumption.
In order to assist the designers and shipyards in their pursuit of the best possible design solutions, FORCE Technology offers traditional iterative optimisation using RANS CFD. Further, we also offer parametric optimisation where the optimisation is performed on an operational profile, typically for two speeds and two draughts selected on the basis of the operational experience from existing vessels of the same size and trade. The hull form will then be optimised using our parametric optimisation tool Friendship Framework combined with RANS CFD.
Today, OSV’s are powered by a range of advanced propulsion systems including ducted propellers, azimuthing thrusters, pod units etc. FORCE Technology has the know-how, procedures and equipment to test and analyse all these propulsion types.
For many OSV’s in general and especially for AHTS’s, the bollard pull is very important as they are often involved in towing operations, e.g. moving of platforms. Both during the initial analysis and the subsequent model tests, the designs must focus on this. Typically, focus is on the duct design, the duct angle, duct mounting on the hull, and design of the aft ship. FORCE Technology has profound know-how when it comes to optimisation of these types of energy-saving devices.
Staying in position
Often OSV’s will interact with other vessels, and therefore it is paramount that the vessels are designed and equipped to maintain position. Today, most vessels are equipped with dynamic positioning (DP) systems to provide propulsion and/or maintain station. Therefore, the designers have to know the capabilities of these systems.
To assess the holding capability, FORCE Technology offers a suite of services ranging from the initial holding capability calculations performed using our tool DPLab, over DP simulations performed using our SimFlex4 simulator, to a complete DP model test performed in our towing tank with a complete thruster and DP system installed in the model. Results of simulations or model tests are analysed to determine the maximum environmental conditions in which station keeping is possible, the power and positioning of thruster units, the required size and the optimum thruster utilisation strategy.
Because of the severe environments in which they often operate, the seakeeping characteristics of OSV’s are crucial to their performance on site. To assess the seakeeping of OSV’s at the early design stage, FORCE Technology employs the linear 3D radiation-diffraction code OMEGA combined with our analysis tool MotionLab. This provides the capability to analyse multiple bodies, wave elevations including diffraction effects, detailed pressure fields and drift forces in a fast and cost-effective manner. Alternatively, analysis can be performed using RANS CFD or model tests.