Ice model testing in HSVA’s large ice tank is the main expertise of the HSVA Arctic Technology department. Several kinds of ships and structures can be tested in all kinds of sea ice features.
Frequently tested vessel types are:
- Ice going merchant ships (tanker, gas tanker, bulk carrier, heavy lift carrier, general cargo vessel, etc.)
- Ice breaking research vessels
- Ice breaking service ships (offshore supply, anchor handler, emergency response)
- Ice breaking inland waterway vessels
Frequently tested fixed structures are:
- Loading tower and terminal
- Jacket structure
- wind generator foundations
- Berthing structures
- Multi-legged GBS
- Artificial islands
- Mitigation and protection structures
Frequently tested floating structures are:
- Ship shape floaters like Drill Ship, FPSO FPU etc.
- Semi submersibles
- Buoy shape floaters
- Spar buoy
Depending on the project demand numerous different set-ups are available. Each project deserves a unique solution regarding set-up and investigations, nevertheless there are certain kinds of test setups that are available by default.
High frequently performed tests are:
Apart from the above listed testing procedures we are always creative in finding new solutions for test set-ups and ice property determination methods. If you have requirements regarding property testing that are not covered by the above listed tests, do not hesitate to contact us for an individual solution.
Brash Ice Tests - Requirements for Light Ice Going Vessels
For ice classed vessels with class notations equivalent to ice class 1C/B/A/A super, the minimum required engine output is defined by the classification society rules (usually based on the “Finnish Swedish Ice Class Rules”). The rules include formulas to calculate the brash ice resistance and required engine power based on few key data of hull geometry and propulsion system.
In case the minimum required engine power is defined by the ice class the rules allow applying alternative methods to determine the required engine output like model tests. As the rule calculations are a quite general approach, the model tests typically result in a lower required main engine power.
Model tests in brash ice determine the required power for an individual ship by taking into account more details of the specific design compared to the rules formulas. HSVA offers these tests which are fully compliant to the rules.
These tests are applicable for all propulsion and hull configurations as twin shaft, podded or CPP propeller. In case of diesel engine directly driving the propulsion train with fixed pitch propeller the model test results (based on stock propeller tests – no manufacture of a design propeller is necessary) and data of the actual design propeller - engine combination are used to check applicable power transmission without violation of the enigne limit.
The results usually show significantly lower resistance and higher propulsion efficiency compared to the outcome of the rules calculation. The report is standardised and can be handed in to the class or authorities to confirm the compliance with the requirements for the determined power.
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Towed Propulsion Tests
During the towed propulsion test the model is connected to the service carriage, which is pushed by the main carriage, via a rigid rod that itself is attached to a load cell at the bows of the model. After being accelerated the model is towed at constant speed. The propeller rpm is changed in four steps from near idling condition through a value close to the self-propulsion point up to a value well above the self-propulsion condition. Both, the thrust of propellers and the coupling force is measured and therefore the actual propulsion point for the given speed can be determined throughout interpolation from linear correlation between thrust and pull force. The resistance can be read from the intersection point of the same curve with the axis of ordinates.
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Free Running Propulsion and Manoeuvering Tests
For the free running test model and carriage are connected only by the cables, which are needed to transfer electrical power into and the measuring signals out of the model. Cables are kept above the model during manoeuvering operations in order to avoid any force application. The model itself is self-propelled while the rpm of each propeller may be remote controlled by throttles from the carriage. For manoeuvering tests, the rudder or azimuth angle can also be controlled by the operator. A motion capture system is used to detect the rigid body motions in all six degrees of freedom. The system uses four cameras installed at the main carriage to detect markers which are located at different positions on the model. Thereby the relative motion between carriage and model may be recorded during the free running tests.
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Fixed Mode Tests
Regardless of the type each model can be tested in fixed mode. This means the models motion is blocked in a number of degrees of freedom. This can be partially e.g. only certain directions of motion are blocked or completely – in this case all six degrees of freedom are blocked. Ice induced vibrations can be investigated in a fixed mode where the model is rigidly connected to the basin floor and only motions in one or two directions is allowed. Ice loads on a vessel may be determined in a fixed setup where the vessel is rigidly connected to the main carriage and pushed through the ice. A special rotation platform allows testing the subject, vessel or structure, under certain oblique angles. In all cases forces in three axes and moments around these axes are determined by means of a six-component-scale. In addition to the forces accelerations, velocities and movements of the structure / vessel will be measured.
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Moored Floating Structures
Moored floating structures can be tested with different test setups in the large model basin of the HSVA. Due to the limited space the mooring system is mostly modelled as a truncated system using either a dry or wet mooring set-up. The mooring characteristic in both setups is simulated by a defined combination of springs and stopper lines.
The wet mooring arrangement is mounted on a submerged framework below the ice sheet which is connected to the main carriage. As the model is connected via stiff lines to the spring packages the model is pushed through the ice. Thereby the ice drift is simulated in reverse by moving the model and not the ice.
The dry mooring system has a similar setup but the spring package is mounted on a frame which is connected to the Y- axis of the carriage. The advantage is that any ice drift direction can be simulated with this setup.
If the floater is equipped with an additional DP system for heading keeping this can be modelled as well by combining the mooring setup with a DP system operating the thrusters. Due to the open architecture the DP-System can either be the HSVA in-house DP or any other operated by for instance the DP system supplier of the actual vessel.
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HSVA owns a DP system designed for DP model testing in open and ice covered water. The DP system can be adjusted to a certain vessel and allows for several kinds of DP tests in model ice. The DP system is a result of a European research project DYPIC – Dynamic Positioning in Ice. It has proved its performance in tens of runs and can either be used in a setup where the ice is pushed through the resting vessel or where the vessel keeps its position relative to the ice tanks main carriage while the carriage moves along the basin.
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