Most of our examples contain a common set of "beginning" commands as well as a common "ending" command. Click here to get documentation for these commands. They will not be discussed directly. The files which are discussed here are:
The entire analysis is done within the Hydrostatics menu which is entered via the command:
$ $********************************************* ENTER HYDROSTATIC MENU $ HSTATICSSetting the inital condition is accomplished with:
$
$********************************************* initial ballast
$
&SUBTITLE NORTH TOW UNDER POWER LINES
&INSTATE -CONDITION 27.5 0 -1.62
&APPLY LIFT-OFF
&COMPARTMENT -PERCENT 8/W 100 7PW 31.82 7SW 32.38 9// 100 9PW 87.75 \
10PW 32.51 10SW 33.06
The subtitle is set to "STG-8" with the command
&SUBTITLE. This command was discussed as one of the
commands common to the "beginning" of files.
The barge condition is set with the command &INSTATE -CONDITION where the three numbers specify the draft, roll, and trim respectively. The loads associated with the name "LIFT-OFF" are applied with the command &APPLY. Having loaded the barge and placed it in the desired condition, we set the initial ballast of the compartments with the &COMPARTMENT command. Ballasting is specified by pairs of data, a compartment selector and a percentage full, e.g. 7PW is a compartment name and 31.82 is the percentage full. We have used some wild characters, /, to select compartments. A / "matches" any character, thus here, 8/W selects tanks 8SW and 8PW to be filled 100 percent. Any final changes in ballast amounts are done with the command &cmp_bal. Then we confirm that the barge system is in equilibrium with the command equi.
For STG-7 the rep_sum macro is used with the -initial option. This is needed so that for later stages the change in ballast arrangement can be determined.
For STG-8 a very similar set of commands are used. This time the graphics that show which compartments were ballasted and which compartments were deballasted will be generated. This is because the rep_sum command was used without the -initial option. For the Lift Off stage the commands to compute longitudinal stress and bending moment are added.
One of the primary things one wishes to accomplish here is to create a ballast plan which minimizes the deflection in the barge. Thus, we next investigate the longitudinal strength of the barge in this condition with:
$
$********************************************* long. strength
$
EQUI
MOMENT -ALLOW 24.00 1.
REPORT
VLIST
PLOT 1 4 -RAX 5 -legend 2 Deflection \
-t_x 'Longitudinal Location (ft)' \
-t_right "Deflection (Inches)' -no
END
rep_sum
For the longitudinal strength results to be meaningful, we first
find the equilibrium position due to these loads with EQUI.
Accelerations are within a prespecified tolerance.
Longitudinal strength is calculated with the command MOMENT.
The option -ALLOW specifies the allowable stress, 24 ksi,
and the allowable deflection, 1 inch. At the conclusion of this command
the user is placed in the Disposition menu.
The standard longitudinal strength report is produced with the
command REPORT, and it gives for each
longitudinal location: the shear force, the bending moment, the
bending stress over allowable, and deflection over allowable.
The command VLIST, short for view list, writes a numbered list of the variables available for selection to the screen, e.g.
The Variables Available for Selection are:
==========================================
1 Long Location 3 Moment 5 Deflection Ratio
2 Shear 4 Stress Ratio
This is quite handy since it allows one to specify what will be plotted,
view, etc. by using the variable's number.
The PLOT command produces a plot with variable 1 (longitudinal
location) as the
independent variable, with variable 4 (stress ratio) on the left axis and
variable 5 (deflection ratio) on the right axis. By using two axes,
both curves will "fill up" the plot. This is what is done with the -t_x
option and the -t_right option in the plot command.
Intact stability is computed via:
$
$********************************************* intact stability
$
&SUBTITLE INTACT STABILITY NORTH TOW
RARM 2.5 25 -ECHO N -WIND 100
REPORT
PLOT 2 6 8 -RAX 10 -legend 2 'WIND HEEL ARM' \
-t_x 'ROLL (DEGREES)' \
-t_right 'RIGHTING ARM (ft)' -no
END
rep_sum
Righting arms are computed with the command RARM. The numbers
The two numbers specify an increment, 2.5 degrees, and a number of
increments, 25, for which arms will be computed.
At each rotation the program will iterate an equilibrium position
for the other degrees of freedom and then compute the righting and wind
heeling arms. The option -ECHO N tells the program that we do not
want to see each equilibrium iteration, and the option -WIND tells
the program to make wind heeling calculations with a wind of 100 knots.
The command REPORT creates the standard righting arm report. This report will show table condition (draft, roll, and trim), minimum height of down flooding points, righting and heeling arms, areas under the righting and heeling arm, the ratio between the two arms, and the net arm. In the table, all the columns will have values which are not consistently zero, except the minimum height of down flooding points column. The down flooding points column will be zero because we did not define down flooding points. The PLOT command produces a plot of the stability results.
Damaged stability is done via the following commands:
$ $********************************************* damaged stability $ &SUBTITLE DAMAGED STABILITY NORTH TOW ..TANK 3PW FLOODED &COMPARTMENT -FLOOD 3PW EQUI &STATUS B_W -HARDThe command &COMPARTMENT tells the program to flood tank 3PW, and then we find the resulting equilibrium with EQUI. A report of the current buoyancy and weight is obtained with &STATUS. Here the B_W is short for buoyancy and weight, and the option -HARD instructs the program to put the report in the output file.
Our next task is to compute a new ballast condition to get back to our original condition with 3PW flooded. This is accomplished with:
&SUBTITLE COMPUTE BALLAST TO REGAIN TOW CONFIGURATION IN DAMAGED CONDITION &INSTATE -CONDITION 27.5 0 -1.62 &STATUS B_W -HARD &STATUS COMPART -HARD &EVENT_STORE 1 &SELECT :COMP -SELECT 7/W 10/W 8// 12// &CMP_BAL H109 :COMP &STATUS B_W -HARDThe &INSTATE command sets the barge back to where we want it to be, and we report the current buoyancy and weight as we did before. The next &STATUS command reports the current compartment properties. We store this situation as event number 1 with the command &EVENT_STORE command. By storing the configuration we will be able to return to it with &INSTATE -EVENT 1. This comes in handy because we now only need to remember one number, the event number, instead of the entire state.
We create a selection criteria called :comp to be used in the ballasting. It selects 7 and 8 wing tanks, and all of the 8 and 12 tanks. The &CMP_BAL command automatically computes the amount of ballast in the selected tanks so that the barge will be in equilibrium at its current location. Here, H109 specifies the body to be ballasted, and :comp defines the compartments to ballast.
Again, we look at longitudinal strength calculations with:
MOMENT -ALLOW 24.00 1.
VIEW -RECORD 1 15 -SEL @
REPORT
END
The only thing new here is the command VIEW
which instructs the program
to print records 1 through 15 of the variables selected by, @, to the
screen.
This wild character, @, stands for any arbitrary number of characters,
so this selection results in all variables being printed.
In the final set of commands we return the barge to the intact condition via the following:
$ $********************************************* restore condition $ &SUBTITLE RETURN TO INITIAL CONFIGURATION NORTH TOW &INSTATE -EVENT 1 &COMPARTMENT -NO_FLOOD 3PW EQUI &STATUS B_WThe command &INSTATE -EVENT 1 returns to that saved as event 1, and &COMPARTMENT -NO_FLOOD 3PW tells the program not to flood tank 3PW.