Simcenter STAR-CCM+ When you perform added resistance analysis in regular bow quartering sea, which DFBI model should be selected?
2024-01-26T20:14:35.000-0500
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Summary
When you performed the added resistance analysis in regular bow quartering sea, you should choice "Planar Motion Carriage" in DFBI.
Details
Calm water, marine resistance analyses are typically modelled using a stationary domain with an incoming flow field, where the water moves around the ship with a prescribed velocity. When looking at added resistance in head waves, the same methodology can be applied, and it is recommended to model at least 20 wave periods.
In the case of other types of sea states, for instance a bow quartering wave in a regular sea, the same approach can not be applied. In this case, we recommend a moving wake tank approach (several articles on this, eg Best Practices for High Speed Craft Resistance Simulations (siemens.com)) as it can make the simulation setup more intuitive and easier to understand.
However, the choice of the DFBI model is not trivial. Depending on the desired motion response, the correct motion module must be selected. Often times, it would be desired to have the prescribed motion in the surge (forward) direction, while pitch, roll, and heave are free while yaw and sway remained fixed.
If free motion is chosen, and roll and pitch are set as free, the ship will still exhibit some undesired yaw motion due to how the Euler angles are computed within the free motion module (.see 4-DoF Maneuvering under self-propulsion (siemens.com)). One remedy is to use multi body motion with an additional body constraint. Another possibility is to use the Planar Motion Mechanism module within the DFBI framework to accomplish this. The planar motion will execute the motion such that yaw and sway can remain fixed, so the desired motion response can be determined.
An example of how to use this module is shown below. In the case of a vessel moving at a constant speed, the planar motion carriage can be used. If acceleration in the forward motion of the vessel need to be simulated, the general planar motion option can be used.
In both figures, the upper left corner represents the resistance, and the upper right corner represents the roll motion.
How to set-up Planar Motion Carriage in DFBI is as follows;
1. You should change to zero speed about “Additional Velocity” in VOF Waves. And “Advancing Direction” has to define.
2. “Body Motion Option” in DFBI is “Planar Motion Carriage”
3. “Planar Motion Option” is “Planar Motion Mechanism”, and “Free Heave, Free Pitch, Free Roll” is True.
4. Ship speed inputs to “Velocity X” in “Planar Motion Mechanism”.
5. “Center of Mass” is as same as “Attachment Point” in “Initial Values”.
Below image shows this methodology produced no yaw.
In the case of other types of sea states, for instance a bow quartering wave in a regular sea, the same approach can not be applied. In this case, we recommend a moving wake tank approach (several articles on this, eg Best Practices for High Speed Craft Resistance Simulations (siemens.com)) as it can make the simulation setup more intuitive and easier to understand.
However, the choice of the DFBI model is not trivial. Depending on the desired motion response, the correct motion module must be selected. Often times, it would be desired to have the prescribed motion in the surge (forward) direction, while pitch, roll, and heave are free while yaw and sway remained fixed.
If free motion is chosen, and roll and pitch are set as free, the ship will still exhibit some undesired yaw motion due to how the Euler angles are computed within the free motion module (.see 4-DoF Maneuvering under self-propulsion (siemens.com)). One remedy is to use multi body motion with an additional body constraint. Another possibility is to use the Planar Motion Mechanism module within the DFBI framework to accomplish this. The planar motion will execute the motion such that yaw and sway can remain fixed, so the desired motion response can be determined.
An example of how to use this module is shown below. In the case of a vessel moving at a constant speed, the planar motion carriage can be used. If acceleration in the forward motion of the vessel need to be simulated, the general planar motion option can be used.
In both figures, the upper left corner represents the resistance, and the upper right corner represents the roll motion.
How to set-up Planar Motion Carriage in DFBI is as follows;
1. You should change to zero speed about “Additional Velocity” in VOF Waves. And “Advancing Direction” has to define.
2. “Body Motion Option” in DFBI is “Planar Motion Carriage”
3. “Planar Motion Option” is “Planar Motion Mechanism”, and “Free Heave, Free Pitch, Free Roll” is True.
4. Ship speed inputs to “Velocity X” in “Planar Motion Mechanism”.
5. “Center of Mass” is as same as “Attachment Point” in “Initial Values”.
Below image shows this methodology produced no yaw.