

April 18, 2024 at 5:46 amnhanani4Subscriber
Hi,
The information of tension leg are diameter 1.2m, thickness 0.04m, length 70m, steel tension leg E =2.1x10^11 N/m2.
Water depth is 80m, wave height 2m, period 6s.
My question is :
1) what formula to calculated axial stiffness at tether boundary condition at fixed point and tether boundary condition on structure?
2) The value of axial stiffness key in at the two (at fixed point and on structure) are can key in same data?
Thank.
Â
Â

April 18, 2024 at 10:48 amShuangxing DuAnsys Employee
(1) The total axial stiffness (K) of a tether is
1/K = 1/K_f + 1/K_s + 1/K_t
where K_f is the axial stiffness at the fixed point (bounday condition at the fixed point), K_s is the axial stiffness at the structure attachment point, K_t is the tether axial stiffness of EA/L.
(2) The axial stiffness values at two boundaries could be the same.

April 18, 2024 at 1:54 pmnhanani4Subscriber
How to calculate the K_f and K_s? What the formula?Â

April 18, 2024 at 2:50 pm

April 22, 2024 at 5:49 amnhanani4Subscriber
What the formula to calculate area of tether mooring? Is it a circle area formula = 3.142 x radius^2?


April 22, 2024 at 8:15 amShuangxing DuAnsys Employee
A=pi/4[D^2(D2*theta)^2]=pi*[Dtheta]*theta, where theta is the thickness, D is diameter.

April 25, 2024 at 9:52 amnhanani4Subscriber
The axial stiffness of tether boundary condition at fixed point and on structure that should be key in.
1)What the formula of axial stiffness of tether boundary condition at fixed point it is right EA/L?
2) What the formula axial stiffness of tether boundary conditionÂ on structure it is right EA/L?
3) or the I should calculate total axial stiffness (1/K = 1/K_f + 1/K_s + 1/K_t) and key in data the Â axial stiffness of tether boundary condition at fixed point and on structure ?Â
4) The valueÂ axial stiffness of tether boundary condition at fixed point and on structure will be same because the data mooring line is same? (tension leg are diameter 1.2m, thickness 0.04m, length 70m, steel tension leg E =2.1x10^11 N/m2)
Â

April 25, 2024 at 11:40 amShuangxing DuAnsys Employee
Please see Aqwa Theory Manual, Section 10.2,
For an installed tether, between the vessel end of the tether and its corresponding vessel attachment point, three spring stiffnesses (,Â , andÂ ) are defined as the inline stiffness and two rotational stiffnesses about theÂ TEAÂ y and zaxes respectively. These are used to determine the relative translational displacement in theÂ TEAÂ xdirection and rotations about theÂ TEAÂ y and zaxes between the vessel end of the tether and the vessel attachment point. The relative translational displacements in theÂ TEAÂ y and zaxial directions are set to be zero at the vessel attachment point.
Similar to the vessel end of an installed tether, three spring stiffnesses (Â ,Â , andÂ ), between the anchor end of the tether and the corresponding fixed point on the sea bed, are defined as the inline stiffness and two rotational stiffnesses about the TEA y and zaxes. The relative translational displacements in the TEA y and zdirections are set to be zero at the anchor point.
And Aqwa reference manual, Section 19.19.2.
For installed tethers, the spring stiffnesses are the inline/vertical stiffness and the two rotational stiffnesses (about the local tether Y and Zaxes) at the ends of the tether. Default values of 1.0E15 are used, if this data record is omitted. A default value of 1.0E15 for the inline stiffness is used if the 1st field is left blank or a negative or zero values is input. For the rotational fields, any value may be entered (except negative values which will be set to zero).

April 28, 2024 at 3:35 amnhanani4Subscriber
can uÂ show the picture again becauseI can not open it,the image can not be load. sorry .

April 29, 2024 at 8:20 am

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