MAX VCG IN Autohydro

Discussion in 'Stability' started by dmetawie, Aug 22, 2009.

  1. dmetawie
    Joined: Aug 2009
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    dmetawie New Member

    Dear Gents,
    While calculating MAXVCG for a drilling rig using Autohydro's MAXVCG Toturial example I get a high deviation from the one previously calculated in the Ops manual, can you please help?
     
  2. Paul Kotzebue

    Paul Kotzebue Previous Member

    I think there is a problem with the AutoHydro MAXVCG command.

    I made a stability submittal to ABS with a MAXVCG curve generated by AutoHydro. I included my AutoHydro RUN file with the submittal. When ABS ran my RUN file using GHS, they got different results. I had to re-submit my calculations using GHS to produce the MAXVCG curve, which matched what ABS was getting.

    ABS had the same GF file I was using. The AutoHydro MAXVCG's were higher then the GHS MAXVCG's.

    I tried running righting arm curves with the VCG set at MAXVCG in both AutoHydro and GHS. GHS hit the stability criteria limits as expected, but AutoHydro did not. Because the AutoHydro righting arm curve matched the GHS righting arm curve, I suspect the problem is in the AutoHydro MAXVCG command.

    I suggest you calculate MAXVCG with softeare other than AutoHydro and see if it matches the ops manual.
     
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  3. bill_boggia
    Joined: Aug 2008
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    bill_boggia New Member

    Max Vcg

    Can anyone recommend a method of calculating MAX VCG in free ship or using annother open source software that will accept export from freeship ?

    (For the multispar structure I have in mind the GHS translator from freeship does not facilitate a correct import)

    Thanks

    Bill :)
     
  4. navalscantler
    Joined: Oct 2013
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    navalscantler Junior Member

    run file for maxvcg for damage criteria

    I have a problem while running the max VCG for damage limit criteria, it is not working on criteria which contain "equ" or gz0 eventhough i have defined the wind pressure for the initial condition, could anyone please share the run file for max VCG for damage criteria?
     
  5. athvas
    Joined: Feb 2013
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    athvas Senior Member

    Can i see your run file command?
     
  6. navalscantler
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    navalscantler Junior Member

    Dear Athvas

    Here is my command run for the max vcg of Autohydro

    read MA.GF

    `clear all previous report
    clear report
    un mt

    note {bold}{center} MAX VCG DATA

    LBP 0 to 410

    wind 0.00001
    hmmt wind /const /gust:1.5

    `setup flooding points
    FLDPT
    FLDPT (1) "Emergency generator room door" 28f, 30.5, 37.1

    `add limit criteria by ICLL CODE
    limit off
    LIMIT (1) ABS ANGLE AT EQU <15
    LIMIT (2) ANGLE FROM EQUIL TO RA0 OR FLD >20
    LIMIT (3) ANGLE FROM EQUIL TO RA0 OR DI >20
    LIMIT (4) RA AT MAX OR 20 > 0.1
    LIMIT (5) AREA FROM EQUIL TO 20 < 0.0175
    LIMIT (6) GM at equil < 10


    `Allowable KG
    Note Set angles from 1 to 40 by 1
    angles 1,2,3,...,40
    `heel 1s
    `GHS 3,3.5,...,20 /KM
    `angles *
    vcg 0.0001

    trim: 0.2a
    maxvcg draft@ms=7,7.5,...,20
    page

    Thank You so much..
     
  7. athvas
    Joined: Feb 2013
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    athvas Senior Member

    plz see below limit criteria command.....

    Limit (1) Abs Angle at Equil < 15
    Limit (2) Angle from Equil to RA0 or FLD > 20
    Limit (4) RA at 20 or Max > .1
    Limit (5) area from equil to 20 > 0.0175

    In limit 5 you have made a mistake in the criteria . It should be greater than not less than. The area under the righting lever curve within this range shall be not less than 0.0175 m.rad.

    I hope it works now...... if not plz revert back. which Autohydro version you are using ?
     
  8. navalscantler
    Joined: Oct 2013
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    navalscantler Junior Member

    Dear Athvas

    I just only activate limit 4 first and it works well and when I activate limit 4, it doesn't work.. this is my problem.. as it can be seen in the command file below

    do you have any run file for the maximum VCG or you have experience in running max vcg with damage criteria, if so, could you please share the run file?

    read MA.GF

    `clear all previous report
    clear report
    un mt

    note {bold}{center} MAX VCG DATA

    LBP 0 to 410

    wind 0.00001
    hmmt wind /const /gust:1.5

    `setup flooding points
    FLDPT
    FLDPT (1) "Emergency generator room door" 28f, 30.5, 37.1

    `add limit criteria by ICLL CODE
    limit off
    LIMIT (1) ABS ANGLE AT EQU < 15
    `LIMIT (2) ANGLE FROM EQUIL TO RA0 OR FLD >20
    `LIMIT (3) ANGLE FROM EQUIL TO RA0 OR DI >20
    LIMIT (4) RA AT MAX OR 20 > 0.1
    `LIMIT (5) AREA FROM EQUIL TO 20 > 0.0175
    `LIMIT (6) GM at equil > 0


    `Allowable KG
    Note Set angles from 1 to 40 by 1
    angles 1,2,3,...,40
    `heel 1s
    `GHS 3,3.5,...,20 /KM
    `angles *
    vcg 0.0001

    trim: 0.2a
    maxvcg draft@ms=7,7.5,...,20
    page
     
  9. navalscantler
    Joined: Oct 2013
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    navalscantler Junior Member

    I use Autohydro version 5.1
     
  10. athvas
    Joined: Feb 2013
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    athvas Senior Member

    see below sample run file..... change/include the parameters according to your vessel details.

    clear report
    Limit off
    Water 1.025
    LBP 40.8F TO 0F
    Limit (1) Abs Angle at Equil < 25
    maxvcg draft@20.4f 2.954 /trim: -0.806/40.8


    Limit off
    Water 1.025
    LBP 40.8F TO 0F
    Limit (2) Angle from Equil to RA0 > 20
    maxvcg draft@20.4f 2.954 /trim: -0.806/40.8


    Limit off
    Water 1.025
    LBP 40.8F TO 0F
    Limit (3) RA at 20 > .1
    maxvcg draft@20.4f 2.954 /trim: -0.806/40.8


    Limit off
    Water 1.025
    LBP 40.8F TO 0F
    Limit (4) area from equil to 20 > 0.0175
    maxvcg draft@20.4f 2.954 /trim: -0.806/40.8
     
  11. navalscantler
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    navalscantler Junior Member

    Dear Athvas

    I have tried as per your above suggestion and unfortunately is doesn't work any more..
    Have you tried this run before?

    if so, could you please share us the run file completely hopefully I can understand if I see the whole steps.. (include the geometry file)

    Thank you so much Athvas
     
  12. athvas
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    athvas Senior Member

    Maybe becoz of the older version... In autoship 6.2 it will work !!!
     
  13. navalscantler
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    navalscantler Junior Member

    Dear Athvas

    Thank you so much for your kind reply, I will look for the later version of Autohydro

    I have another question, I want to have a maximum vcg for my current condition only which means that I am looking for one VCG for my current draft and trim, my command is

    `implement IMO A749
    limit off
    limit(1) area from 0 to max at 15 > 0.070
    limit(2) area from 0 to max at 30 > 0.055

    variable drx
    variable trx

    solve draft

    set drx = draft
    set trx = trim

    angles 1,2,3,...,40
    Maxvcg draft {drx} /trim:{trim}

    note maxvcg

    but it doesn't work, could you please check this.. I want to pick variable for current draft and trim.. Is it correct?

    Thank You so much..
     
  14. athvas
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    athvas Senior Member

    In the below command, put your values
    xxxx - Your current draft
    yyyy - Your current trim

    40.8 is the LBP - Put your LBP value
    20.5 is the draft location at midship - Put your location at midship (mid of LBP)

    -----------------------------------------
    clear report
    Limit off
    Water 1.025
    LBP 40.8F TO 0F
    Limit (1) area from 0 to max at 15 > 0.070
    maxvcg draft@20.5f xxxx /trim: yyyy/40.8
     

  15. navalscantler
    Joined: Oct 2013
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    navalscantler Junior Member

    does it mean I have to define it by my self, I want to let the program determine it by itself since I have many cases that I have defined..

    If so it means I have to define xxx manually..

    Thank you so much Anthvas
     
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