[antieskmartin]

Hi everyone,

I am working on the propulsion of a ship using flapping foil mounted at the bottom of the hull (PFA Image 1).

I already simulated the movement of the vessel due to flapping motion of foils in Star CCM+. Now, trying to simulate the movement of the vessel due to simultaneous flapping and translation of foils (PFA the Video). But I could not find any options to add translation motion.

https://www.youtube.com/watch?v=lI9wk3d8I_Q

[ping]

an overset mesh region will do this nicely since you can prescribe any forced motion to that region

[antieskmartin]

Hi Ping,

Thank you very much for the reply

Yes, I have used superposed rotation motion for the flaps which are inside individual overset region. And it works.

But I want to assign rotation as well as translation motion to the flaps which can not be done using superposed rotation (as far as I know).

I am in search of a motion model which can give both translation and rotation to the flaps and the thrust produced by the flaps should move the ship forward.

Can you please explain your answer based on this?

[ping]

ignore superimposed rotation and instead use simple forced rotation and translation motion were you can arbitrarily include both forms of movement

[antieskmartin]

Hi Ping,

Again, thanks for the reply.

If I choose simple 'Rotation & Translation', I am sure that the flap will execute the motion as I input the parameters.

But, will it move the vessel forward?

I feel that in such a case, the flap will keep oscillating, but the thrust produced by the oscillation may not move the ship forward.

[ping]

your need to create a force report and then use this force as an external force applied to the hull dfbi body

[antieskmartin]

Hi Ping,

thanks again for your reply.

I will try the simulation with force rotation and translation.

Along with that during the time when I simulated the foil alone(open water

condition) which undergoes both translation and rotation. I have noticed that

the foil is slowly moving in the X direction(where x direction motion is

restricted). Actually, I have confused why it is happening. At the start of the

simulation both the lab and managed coordinates are at the same point.

After iterating it seems there is slight change in the position of managed

coordinates while the lab coordinate is at the same location. I am attaching

the link of images

1.initial foil image.
https://antieskmartin.blogspot.com/2...tial-foil.html

2.foil after simulation.
https://antieskmartin.blogspot.com/2...imulation.html

3.Motion details
https://antieskmartin.blogspot.com/2...n-details.html


Could you please help me in figuring out the problem.

Thanks in advance.

[ping]

sorry it is not as easy as i expected since because that type of motion is not dfbi you cant lock motion in say the x direction
there is probable a good way to do it but I cant think of it at present so the hard way is to measure x motion eg acceleration and apply the reverse force to cancel this out

[antieskmartin]

Thanks ping

I will try with this idea.

[ping]

i have create a model to show that what you require is quite possible but it is not for a beginner in star and have attached some short animations of the resulting run

. based on boat in waves tutorial which was remeshed using the trimmer and still in half model mode
. added a overset mesh region containing a flapper with some mesh refinement in the background boat hull region to ensure good cell size matching across the overset interface
. add reports of the hull 6dof body z direction (Hull_Vz) and y rotation (Hull_Wy) velocities which are needed to drive the flapper motion in unison with the hull sink and trim
. did not drive/force the hull with the flapper - this can be done by using the self propulsion technique so see that relevent tutorial

. create 3 new nested coordinate systems under the hull body coordinate system
... the first called cs1 is simply an exact copy of the hull one so it follows the full motion
... the second called cs2 is under cs1 and again has the same properties as cs1
... the last called cs3 is under cs2 and has its origin at the center of rotation of the flapper

. now create the motion method to drive the flapper
... create a new translation motion with velocity set to [0.0, 0.0, ${Hull_VzReport} - (4 * cos($Time*12.56))] in cs1 and managing cs2 - this causes the flapper to follow the hulls z motion and also drives the separate up and down motion of the flapper
... below that create a superimposed rotation motion about -y axis with velocity ${Hull_WyReport} in cs2 and managing cs3 - this causes the flapper to follow the hulls y rotations
... below that create a superimposed rotation motion about y axis with velocity (-4 * sin($Time*12.56)) in cs3 - this rotates the flapper about its local cs3
. apply this last superimposed motion to the flapper region to force its motion to have all these superimposed components

used simple sinusoidal motions and these can be subsituted with more complex wave shapes to get better driving forces

[antieskmartin]

Hello Ping

Thank you so much for your information, I will try with this and let you know.

[antieskmartin]

Hello Ping

Could you please give your email ID

[antieskmartin]

Hello Ping

It is working for me. But the foil is moving out of overlap region and causing
error.?

So,how did you restrict the motion in X direction?

Could you please explain that also?.

Thanks in advance.

[sohrabmajd]

Originally Posted by ping

i have create a model to show that what you require is quite possible but it is not for a beginner in star and have attached some short animations of the resulting run

. based on boat in waves tutorial which was remeshed using the trimmer and still in half model mode
. added a overset mesh region containing a flapper with some mesh refinement in the background boat hull region to ensure good cell size matching across the overset interface
. add reports of the hull 6dof body z direction (Hull_Vz) and y rotation (Hull_Wy) velocities which are needed to drive the flapper motion in unison with the hull sink and trim
. did not drive/force the hull with the flapper - this can be done by using the self propulsion technique so see that relevent tutorial

. create 3 new nested coordinate systems under the hull body coordinate system
... the first called cs1 is simply an exact copy of the hull one so it follows the full motion
... the second called cs2 is under cs1 and again has the same properties as cs1
... the last called cs3 is under cs2 and has its origin at the center of rotation of the flapper

. now create the motion method to drive the flapper
... create a new translation motion with velocity set to [0.0, 0.0, ${Hull_VzReport} - (4 * cos($Time*12.56))] in cs1 and managing cs2 - this causes the flapper to follow the hulls z motion and also drives the separate up and down motion of the flapper
... below that create a superimposed rotation motion about -y axis with velocity ${Hull_WyReport} in cs2 and managing cs3 - this causes the flapper to follow the hulls y rotations
... below that create a superimposed rotation motion about y axis with velocity (-4 * sin($Time*12.56)) in cs3 - this rotates the flapper about its local cs3
. apply this last superimposed motion to the flapper region to force its motion to have all these superimposed components

used simple sinusoidal motions and these can be subsituted with more complex wave shapes to get better driving forces

Hello
I read your description of the foil movement in star ccm. I want to do this in CFX. Can you explain the relation of motions?
What does $ mean?
Do you know how to report body movements on axes in CFX?
help please

[ping]

$something is a reference to an existing field function in star which gives you a field value eg velocity in every cell and you can create your own user variables too and so do calculations and then use these for display and reporting locally or globally.
i have no idea how to do this in cfx

[sohrabmajd]

Originally Posted by ping

$something is a reference to an existing field function in star which gives you a field value eg velocity in every cell and you can create your own user variables too and so do calculations and then use these for display and reporting locally or globally.
i have no idea how to do this in cfx

thanks ping