The art of lying completely still
For advanced offshore operations, position-keeping becomes more and more important.
For example, placing a large wind turbine on a water depth of up to 30 metres puts heavy requirements on the hardware (rudders, propellers and thruster units) and Dynamic Positioning software onboard the vessel.
Similarly, Dynamic Positioning (DP) Drilling platforms are today used in harsher environments than previously, thereby putting heavier requirements on the DP capability of the platforms. Since the early 1980’s, FORCE Technology has performed R&D within DP. Our experience is rooted in DP of drilling platforms and other offshore structures and vessels.
When the offshore wind turbine areas have been expanding, our knowhow has been used in a large number of projects with wind turbine installation vessels and service vessels. Through our knowledge and experience, FORCE Technology has developed three different services within DP. These three services offer different knowledge of the operational constraints and can be used both individually and in connection with each other.
Similarly, Dynamic Positioning (DP) Drilling platforms are today used in harsher environments than previously, thereby putting heavier requirements on the DP capability of the platforms. Since the early 1980’s, FORCE Technology has performed R&D within DP. Our experience is rooted in DP of drilling platforms and other offshore structures and vessels.
When the offshore wind turbine areas have been expanding, our knowhow has been used in a large number of projects with wind turbine installation vessels and service vessels. Through our knowledge and experience, FORCE Technology has developed three different services within DP. These three services offer different knowledge of the operational constraints and can be used both individually and in connection with each other.
DPLab – Static Holding Capability
Embarking on a new project with a dynamically positioned ship or platform immediately poses the following three questions once the site has been:
- Is station-keeping possible under the anticipated conditions?
- What sizes of thrusters are required, and where do we install them to maximize our station-keeping capability?
- How are the thrusters best utilised?
These three problems do not, of course, have independent solutions, instead a common solution solving all three must be found. FORCE Technology has developed the Holding Capability Module for the DPLab software for inhouse use or as software sold in a package with wind & current predictions or wind tunnel model tests. The program follows the recommendations of IMCA M 140.
The tool performs static calculations, balancing the available thrust and the environmental forces. The holding capability is defined as the limiting environmental (arising from wind, current and waves) forces that can be balanced by the vessel using its propulsive systems in an optimal way. DPLab has been sold to leading Asian shipyards and a number of consultants world-wide.
Time Domain Simulations
While DPLab provides only a static picture, FORCE Technology also offers dynamic possibilities in our simulators where it is possible to perform DP simulations with varying degrees of current, wind and waves. The core of the simulations is the in-house developed DENMark1 model which is acknowledged to be the most accurate mathematical model with regard to maritime simulation. With the time domain simulations you find out how precisely it is possible to keep the needed position under the influence of wind, current and waves. Furthermore, the time domain simulations in six degrees of freedom provide a strong indication of the motions of the ship during operation.
DP Model Tests
The final service FORCE Technology offers within DP is scaled model testing. During these tests, thrusters, propellers and rudder are tested together with the DP system. These tests give a very realistic representation of the precision you could expect during your actual DP operation.
Besides this important knowledge, the tests also include effects such as green water, slamming and advanced wave systems which are hard to copy in numerical simulations. The DP tests can be performed with our in-house DP system or with a vendor-provided DP system. Through a model test you also get all the dynamic and non-linear effects. Thereby, model tests offer a more precise representation of the ship’s ability to hold the position during operation.
Model tests are usually preferred when the design is locked, and the DP capacity is to be documented. To be able to perform DP model tests, FORCE Technology has prepared a series of advanced model thruster units. The units are controlled via advanced EPOS controls and are able to measure heading, RPM and the delivered thrust from each thruster unit. The development has taken place over the last 20 years, and our model thruster units are now in their 3rd generation and available for both integration into semisubmersible hulls and deck mounting on monohull vessels such as drilling vessels.
