Learning Forum

[1317794602]

How to add a spring device between the two structures of AQWA, so that it will receive force when compressed or stretched

[Shuangxing Du]

You can define a linear cable with the Unstretched Length to be zero.

[1317794602]

 thanks But cable compression doesn't apply force

[Shuangxing Du]

Please run the two files below, you could find the force on the spring is non-zero for these two cases of which the constant forces (defined by FORC data record) are in the opposite directions. 

(1) ABT001.DAT

OB T001  LIBR  STAT
TITLE               point mass with a zero unstretched spring
OPTIONS PBIS REST END
RESTART   1  5
    01    COOR
    01   1                 0.0       0.0       1.0
    01   2                 0.0       0.0       2.0
 END01 
    02    ELM1
 END02PMAS          (1)(1)(1)(1)
    02    FINI
    03    MATE
 END03             1      10.0
    04    GEOM
 END04PMAS         1      20.0       0.0       0.0      20.0       0.0      20.0
    05    GLOB
    05DPTH     250.0
    05DENS    1025.0
 END05ACCG     9.806
    06    FDR1
    06PERD    1    6      18.0      17.0      16.5      16.0      15.0      14.0
    06PERD    7    7      12.0
 END06DIRN    0    5    -180.0     180.0
    07    NONE
    08    NONE
    09    NONE
    10    NONE
    11    NONE
    12    NONE
    13    NONE
    14    MOOR
* INITIAL DISTANCE BETWEEN TWO ATTACHMENTS IS ZERO, UNSTRETCHED LENGTH IS ZERO
    14LINE    1    1    0    1     1.0E5       0.0
    14FORC    1    1    0    2    -1.0E3
 END14
    15    NONE
    16    LMTS
    16MXNI        20
 END16MERR                0.01      0.01      0.01      0.01      0.01      0.01
    17    NONE
    18    PROP
 END18PTEN

(2) ABT0002.DAT

JOB T001  LIBR  STAT
TITLE               point mass with a zero unstretched spring
OPTIONS PBIS REST END
RESTART   1  5
    01    COOR
    01   1                 0.0       0.0       1.0
    01   2                 0.0       0.0       2.0
 END01 
    02    ELM1
 END02PMAS          (1)(1)(1)(1)
    02    FINI
    03    MATE
 END03             1      10.0
    04    GEOM
 END04PMAS         1      20.0       0.0       0.0      20.0       0.0      20.0
    05    GLOB
    05DPTH     250.0
    05DENS    1025.0
 END05ACCG     9.806
    06    FDR1
    06PERD    1    6      18.0      17.0      16.5      16.0      15.0      14.0
    06PERD    7    7      12.0
 END06DIRN    0    5    -180.0     180.0
    07    NONE
    08    NONE
    09    NONE
    10    NONE
    11    NONE
    12    NONE
    13    NONE
    14    MOOR
* INITIAL DISTANCE BETWEEN TWO ATTACHMENTS IS ZERO, UNSTRETCHED LENGTH IS ZERO    
    14LINE    1    1    0    1     1.0E5       0.0
    14FORC    1    1    0    2     1.0E3
 END14
    15    NONE
    16    LMTS
    16MXNI        20
 END16MERR                0.01      0.01      0.01      0.01      0.01      0.01
    17    NONE
    18    PROP
 END18PTEN

[1317794602]

Of these four hinge points, you can run time domain analysis if you open three of them, but four will report an error, how to solve this

[1317794602]

[1317794602]

this is error

[1317794602]

On the far right is a buoy, in the middle is an approach bridge, and on the left is a wall

[Shuangxing Du]

Your model has redundant constraint. To avoid the error, please do

(1) if the top and bottom bridges are modelled by two structures, defineing two ball/sockets to link bridges and buoy, defining two hinges to link bridges and wall.

(2) if the top and bottom bridges is modelled by one structure, defineing one hinge between wall and bridge structure, and defining another hinge between bridge structure and buoy.

 

[1317794602]

thanks！

 

[1317794602]

Hello, I have created a hinge joint. When analyzing the force, how can I determine the direction of XYZ? Is this force direction in the original coordinate system（FRA）

[1317794602]

[1317794602]

Is the force acting on the hinge point the force acting on the hinge point or the force it exerts on the structure

[Shuangxing Du]

The force and moment act on the hing point as Joint Forces, these force/moment provide the force and moment as Structure Force, Articulation Sum Only with respect to the COGs of the linked structures. As shown below both the joint force and the articutation sum force on the linked structure can be displayed in Aqwa Workbench.

[1317794602]

Does this result indicate the positive or negative force on the hinge point or the positive or negative force on the structure from the hinge point

[Shuangxing Du]

yes, you are right.

[1317794602]

Does this direction represent the direction in which the hinge point gives force to the structure?

[Shuangxing Du]

Yes, it is represented in the global fixed axes.

[1317794602]

thanks

 

[1317794602]

Hello, my wind speed in AQWA was imported into an Excel file, and the wind speed has a duration of 10800 seconds. As wind speed can cause changes in flow velocity, how should I set this flow velocity based on this wind speed

 

[Shuangxing Du]

The effect of wind on the ocean current could be the topic of the oceanic and atmospheric study.  Could you please find some solutions on the problem, and define the corresponding current velocity in Aqwa analysis?

[1317794602]

I want to set the flow rate to change over time. Can this aqwa be achieved

[Shuangxing Du]

I am sorry that it may not possible to set the current to change over time in Aqwa.  But you may run several time durations, the current are different between different durations.

[1317794602]

I want to study the forces acting on the two hinge points on the right in the XYZ and RX directions. This requires limiting the movement of the middle two floating bodies in the RX direction. So, how do I add hinges to these four hinge points? I have used two BALLs and two hinges, but I cannot study the force in the Rx direction. Thank you for your answer

[Shuangxing Du]

It is a statically indeterminate configiration. Aqwa could provide the precise structural responses of these floating bodies and bridges, but may not give the accurate reaction forces on the redundant hinges.