Learning Forum

[r.abbasi]

I am trying to model a linear connection with spring-damper characteristics, similar to a Power Take-Off (PTO) system, for a structure in AQWA. From my understanding, it's possible to use a cable with defined stiffness to model the spring behavior, but I haven’t found an option to incorporate damping.

To provide more context, the structure I am working with has a submerged section and is connected to a linear damper that only allows movement in the heave direction.

Could you advise on how to model the damping effect in AQWA?

i tried to use two fenders in different directions, but I don't know how!

 

 

[Shuangxing Du]

Please use 8 fenders on two horizontal levels to restrict motions except heave, and use another two fenders along vertical axial direction to simulate the damping/stiffness of a Power Take-Off (PTO) system.

[r.abbasi]

could you please check is any difference between this method or define additional damping like what is attached?

[r.abbasi]

I would appreciate knowing what details we need to input for the fenders in the method you explained, such as the information shown below:

Because the amount of damping we require is just a linear damper.

[Shuangxing Du]

Please read 5.8.5. Fenders (ansys.com)

[r.abbasi]

Thank you for your guidance. I followed the procedure as shown below (top view):

"I don't know if the setup is correct or not, but when I define them, the float does not stay in place and behaves as shown below:

[Shuangxing Du]

Please check the normal direction of the fender, which should be pointed towards the fixed point.

[r.abbasi]

Thank you for your guidance. I would appreciate it if you could help me understand the following questions as well:

1. Can we simulate the damping/stiffness of a Power Take-Off (PTO) system using just two fenders along the vertical axis, deactivating other degrees of freedom (DoF), instead of using eight fenders on two horizontal levels to restrict motions?

2. If we want to use a linear damper with no stiffness, such as a 5 N·s/m damper, what values should we input for the damping coefficient (with units in seconds) and for coefficient A (with units in N/m)?

[Shuangxing Du]

From 9.8.3. Fender Friction and Damping (ansys.com), equation (9.89), you may need to define a very small stiffness, for example k=1.0e-3 N/m, the input fender damping coefficient is 5 N.s/m / k = 5 N.s/m /1.0e-3 N/m = 5e3 s.   

[r.abbasi]

Thank you for your guidance, I just need to be sure that is the direction of the fenders corret? (always one in compression )

If we make the fenders' size longer, will it affect the output force?

[Shuangxing Du]

From 9.8. Fender (ansys.com)

The force is the function of the length change, instead of the initial uncompressed size.