Learning Forum

[bengalili]

Hi. 

I want to conduct a hydrostatic analysis on a Cylinder from the sea surface to the sea depth. 
I need to get the force and moment exherted on the cylinder. 
1. It works but in the LIS file I get very low (almost Zero) moment and force.
2. I also want to make sure that the moment is calculated arround the sea floor. 
3. how do I control the drag coefficient and added mass coefficient?

Appriciate the help. 

example:
Diameter - 1m
sea depth - 5m
Wave period - 10 sec

JOB 0001  LINE
TITLE               CYLINDER MODEL
OPTIONS LDOP GOON REST END
RESTART   1  3
    01    COOR
    01   1                 0.0       0.0       0.0
    01   2                -0.5       0.0       0.0
    01   3                -1.0       0.0       0.0
    01   4                -1.5       0.0       0.0
    01   5                -2.0       0.0       0.0
    01   6                -2.5       0.0       0.0
    01   7                -3.0       0.0       0.0
    01   8                -3.5       0.0       0.0
    01   9                -4.0       0.0       0.0
    01  10                -4.5       0.0       0.0
    01  11                -5.0       0.0       0.0
    01 999                 0.0       0.0      -5.0
 END01
    02    ELM1
    02TUBE          (1)(1)(2)(1)(1)
    02TUBE          (1)(2)(3)(1)(1)
    02TUBE          (1)(3)(4)(1)(1)
    02TUBE          (1)(4)(5)(1)(1)
    02TUBE          (1)(5)(6)(1)(1)
    02TUBE          (1)(6)(7)(1)(1)
    02TUBE          (1)(7)(8)(1)(1)
    02TUBE          (1)(8)(9)(1)(1)
    02TUBE          (1)(9)(10)(1)(1)
    02TUBE          (1)(10)(11)(1)(1)
 END02
    02    FINI
    03    MATE
    03             1     7800
 END03
    04    GEOM
    04TUBE         1       1.0       0.1         0.0
 END04
    05    GLOB
    05DPTH     5.0
    05DENS    1025.0
    05ACCG     9.806      
 END05
    06    FDR1
    06PERD    1    1      10.0
    06DIRN    1    3    -180.0       0.0     180.0
 END06
    07    WFS1
 END07
    08    NONE


LIS OUTPUT:

 

[Shuangxing Du]

In your nodal coordinate defintion (Node#1 ~ Node#11) and the tube element definition,  the tubes' axial axis is on the mean water surface and  along x-direction.  

The force and moment are output with respect to the COG of the structure, i.e. (Xg, Yg, Zg).  If you want the moment to be output with respect to another reference point, i.e. (Xr, Yr, Zr),  please manually do the calculation with the additional cross product term:

(Mrx, Mry, Mrz) = (Mx, My, Mz) + (Xr -Xg, Yr-Yg, Zr-Zg) x (Fx, Fy, Fz)

where (Mx, My, Mz) is the moment with respect to COG, (Fx, Fy, Fz) is the force with the respect to COG.

The translational drag and added mass coefficients can be input by CONT data record, see below and see 8.3. Geometric Property Data Record (ansys.com)