Good morning,
I'm running a mooring analysis and it is happening something I didn't expect: when I create the connectors (ropes), they have a magnitude more than 0. It is happening with no environmental loads. Only when I use "l_tension 0" do they turn back to 0 Magnitude value. I think something is missing because the model is in equilibrium, but the system is no more stable with the connectors. Can you help me to understand the reason why it is happening?
TEST.dat
$********************************************* set basics &DIMEN -DIMEN METRES M-TONS &TITLE TMI&DBA MOORING &set use_obs = .true. $ METTO VERO PER AVERE INTERAZIONE TRA vessel/quay/fenders $ $ read model INMODEL &EQUI MEDIT $TMI - QUAY DIMENSIONS &SET L_TMI = 90.00 &SET B_TMI = 16.30 &SET DR_TMI = 2.00 &SET B_QUAY = 1.20 &SET H_QUAY = 7.50 $ TMI FENDERS QUAY SIDE &SET A_TMI = (0.1*%L_TMI) &SET M_TMI = (0.5*%L_TMI) &SET F_TMI = (0.9*%L_TMI) $ FENDERS &SET Xs1 = 40 &SET Xm1 = 1850 &SET Ys1 = 74 &SET Ym1 = 1850 &SET Zs1 = 1 &SET Zm1 = 300 &DESCRIBE BODY GROUND -NOTE QUAY $BOLLARD ON QUAY *A 58.0 13.0 4.5 *B 29.0 15.0 4.5 *C 11.7 13.0 4.5 *D -11.7 11.3 4.5 *E -38.8 11.3 4.5 *F -64.2 11.3 4.5 *G -88.5 11.3 4.5 *H -119.4 11.3 4.5 *I -36.1 23.0 4.5 *L -100.0 23.0 4.5 $FENDERS ON QUAY TMI SIDE *FQ1 -%(A_TMI) 10.15 0.0 $7.5 *FQ2 -%(F_TMI) 10.15 0.0 $7.5 $*FQ3 %(M_TMI) 10.15 0.0 $7.5 &DESCRIBE BODY TMI $FENDERS ON TMI *FT1 -%(A_TMI) 10.15 2.5 *FT2 -%(F_TMI) 10.15 2.5 $*FT3 -%(M_TMI) 10.15 2.5 ~FENDER gspr compression x %(Xs1) %(Xm1) y %(Ys1) %(Ym1) z %(Zs1) %(Zm1) -FRICTION 0.2 CONNECTOR Y_A ~FENDER *FT1 *FQ1 -EULER 0 0 -90 CONNECTOR Y_F ~FENDER *FT2 *FQ2 -EULER 0 0 -90 $CONNECTOR Y_M ~FENDER *FT3 *FQ3 -EULER 0 0 90 *T1 -1.5 -7.5 5.0 *T2 -0.4 -7.5 5.0 *T3 -0.4 7.5 5.0 *T4 -1.5 7.5 5.0 *T5 -46.5 7.5 5.5 $RELOCATED *T6 -67.5 7.5 5.0 *T7 -88.5 7.5 5.0 *T8 -89.6 7.5 5.0 *T9 -89.6 -7.5 5.0 *T10 -88.5 -7.5 5.0 ~RO26 h_cat 36 -b_tension 26 -EMODULUS 2088 ~RO17 h_cat 36 -b_tension 17 -EMODULUS 1365 CONNECTOR RO1 ~RO26 *T1 *B CONNECTOR RO2 ~RO17 *T2 *B CONNECTOR RO3 ~RO17 *T3 *C CONNECTOR RO4 ~RO26 *T4 *D CONNECTOR RO5 ~RO26 *T5 *E CONNECTOR RO6 ~RO26 *T6 *G CONNECTOR RO7 ~RO26 *T7 *F CONNECTOR RO8 ~RO17 *T8 *F CONNECTOR RO9 ~RO17 *T9 *H CONNECTOR RO10 ~RO26 *T10 *H END_MEDIT &EQUI &STATUS Force &STATUS F_CONNECT &STATUS LINES
Hi Pietro,
Your problem statement was accompanied by the file test.dat. Can you also provide the command file?
But let me try to advance the conversation.
Here are things I would check.
Report the distance between the nodes used to define the rope. Use the &point(d_node *node) command. Is the rope length longer than the reported distance?
How are you defining the rope? Does it have self weight?
Are you using h_cat or b_cat?
In general working with a value of 0 can cause difficulties. Inside the source code we have put in many check for 0. We try to avoid dividing by 0. The value you are seeing might be due to this. If you want the force to be dependent only on the distance between the two nodes, there is the sl_elem. This element can be defined to have zero tension.
I hope this helps. I hope to hear from you.
Georgina Maldonado
Hi Georgina,
The command file is the "TEST.txt", I had to change the extension since I was not able to upload the same. I'm using h_cat. In the main time, I'm trying to get the distance between the nodes.
Thanks in advance
Pietro
test.zip
The attached zip file has a changed test.cif. I left a note, "Pietro look here". For element R01 the rope length is 26. The distance between the nodes is 36. That is why there is tension in the rope.
I hope this helps.
georgina
Sorry, but I'm a little bit confused.
I understood how you calculate the distance between points *T1 and *B, which is 38m. Regarding the rope length, looking at the Manual I read the following.
QUOTE
The -B_TENSION option is used to define a breaking tension, BTEN (bforce),for each segment of the connector. If this option is not specified, then one will becomputed based on the area of the element and the ultimate tensile stress. Thisvalue is used to normalize the tension, to report a unity check, and in some casesto compute fatigue.
UNQUOTE
-b_tension should not be the rope length, so why the rope is 26m?
Thanks
Now I see what you are getting at. :-)
Please add the -len option to the class definition. Since MOSES did not find a length it picked up any number it saw. Below is the suggested change.
~RO26 h_cat 36 -len 37 -b_tension 26 -EMODULUS 2088~RO17 h_cat 36 -len 37 -b_tension 17 -EMODULUS 1365
If you do not want to use the -len option then you will have to use the
&connector -l_tension cname
command to get a tension of 0.
Georgina