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Active Heave Compensation

  1. Feb 14, 2012 #1
    For my master's thesis I've been given the assignment to design an active heave compensation system for a mobile shipboard crane.
    The problem is that I have very little information about the crane itself. There's little or no information about the hydraulic cylinders for example, materials used, only vague dimension of the crane, so the design would be mainly theoretical.

    So far I've found very little information about mobile crane design, even in the library of the University of Delft, so I was wondering if anyone could help.

    The main principle is similar as the one used by Ampelmann in their dynamic platform: http://www.ampelmann.nl/index.php?id=93.
    A Motion Reference Unit detects the ship movements, and these signals are processed and used to control the hydraulic cylinders.
    My job would be to theoretically calculate the stresses and acceleration forces on the crane tip, and control the hydraulic cylinder of the first crane arm to counter the wave movements.
    In order to do so, I'd need more information about how to calculate the stresses on a crane structure.

    Any information on the heave compensation principle or on the workings and construction of a mobile crane is more than welcome.

    Kind regards,

    Wouter

    wouterdg@gmail.com
     
  2. jcsd
  3. Feb 14, 2012 #2

    russ_watters

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    Staff: Mentor

    I find it hard to believe a crane manufacturer would be unwilling to help you, but even if they are, why not find an actual crane to analyze?
     
  4. Feb 14, 2012 #3
    The mobile crane is from an italian manufacturer named Heila. I contacted them a couple times, but they didn't reply. I contacted their distrubutor in the Netherlands but they only had a very basic Acad plan, no actual production plans.
    I've also tried contacting Liebherr and Huismann, other crane manufacturers, but haven't received any answers from them either.

    The company that bought the HEILA crane, and for which I'm doing the research has no info on the crane itsself, only order numbers of parts which are pretty useless

    If you know a company that would be willing to provide some detailed information, I would be more than willing to contact them.

    Thanks
     
  5. Feb 14, 2012 #4
    Offshore cranes are typically certified by DNV; a good place to start might be to look for relevant codes of practice https://exchange.dnv.com/publishing/ServiceDocs.asp [Broken]

    This should help out with calculating relative crane tip velocity etc. Have you considered the application of strain gauges & accelerometers to instead of a theoretical approach?

    If you are working for the company that purchased the crane then there must be drawings, manuals etc. maybe chase them a bit harder.

    As a tip, if you're contacting companies pose as a interested person & not a student looking for free advice. They will probably be a little more receptive.
     
    Last edited by a moderator: May 5, 2017
  6. Feb 15, 2012 #5
    Thanks Crobb, I'll have a look into those DNV codes.

    I have considered strain gauges in the hook of the crane, and an MRU to measure the ship's angular and vertical movements. These signals can be sent to a motion controller and used to control the movement of the hydraulic cylinders of the crane to compensate for the vertical heave motion and possibly roll/pitch of the ship. I still need to find more detailed information about the workings of the internal heave compensation process, algorithm-wise. I know labview and matlab are able to simulate wave movements, and can be used to build a dynamic model, but my knowledge of matlab and labview so far is pretty non existent.

    First I wanted to focus on the crane itself, and if and how the structure and hydraulics can handle the current overload stresses due to dynamic ship movement. This photo can give you an idea how the crane looks like:
    http://i280.photobucket.com/albums/kk175/chevyvan1989/Foto003-17.jpg [Broken]
    2 arms operated by two cylinders, and 2 extensions with one cylinder each. I was hoping to find examples of static and dynamic calculations. Even if only with the slightest resemblance.

    Furthermore, even the assistant of hydraulics at my school can't completely explain the hydraulics in the schematics. If someone would like to take a shot at it, please feel free to do so, and send me an email, I can forward you the schematics.
     
    Last edited by a moderator: May 5, 2017
  7. Mar 30, 2012 #6
    Dear Wouter,

    Hi, i have being reading those posts, i may suggest you to do not use the offshore regulations, as i have seen the picture i may believe this specific utilization of the crane i may say is for harbor conditions, if you talk about an offshore you need to consider a different dynamic factor ( this could change based on the certification authority, which means the rules [specifically dnv as i saw above]), however the AHC can be applied to dredging cranes, and i think that HEILA has for sure (must!!) provided as well AHC cranes for dredging cranes.
    I went to their website and i saw the applications of the offshore cranes, i think that mostly offshore cranes have different configurations, as knuckle boom or telescopic...etc...
    personally i do not think there are many of the dredging cranes for offshore applications, but i am not the expert to say so

    Those are mostly used into harbor conditions, however im not that expert to know wether are used as well in offshore conditions...
     
  8. Mar 30, 2012 #7

    Bobbywhy

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    Gold Member

    Last edited: Mar 30, 2012
  9. Apr 1, 2012 #8
    Hi Waled Gaber,

    The crane is used on a ship that assists cutter and suction hopper dredgers, so the boat and cranes go anywhere the ships go. This is indeed usually in coastal and harbour regions, but the occasional tanker that passes by, can lead to bigger waves, and bigger dynamic loads on the crane. So I do need to introduce some kind of dynamic factor. I was looking in Lloyd's Register's Code for lifting appliances, and they indeed make a clear distinction between offshore cranes and shipboard cranes in harbours.
    However, since the crane was designed for harbour conditions, and damage still occurs a bit too frequent, I was going to take a look at factors used in offshore industry for crane derating and use those for inspiration.

    HEILA indeed recently introduced AHC and ways of visual and auditory overload feedback on their new crane models. The old ones aren't as 'smart' however. I'm sure they would provide retrofits as well, but unfortunately their company dodges every email or phonecall I make :)

    In the end, we're probably just going to fit the crane with a load moment indicator and derate it using the ship's motions and the sea states... If you've got any experience in this field, or information, feel free to share :)
     
  10. Apr 13, 2012 #9
    Dear Kipp,

    i suggest you to use a dynamic factor of 1.3 for harbour condition. that one should do well.
     
  11. Apr 13, 2012 #10
    Dear Kipp,

    i am interested to know your studies more and as well about your activities. may i know more about those?
     
  12. Apr 14, 2012 #11
    Dear Waled,

    My studies lie in the field of electromechanical engineering, with a brief spin-off into the maritime industry with this thesis. My spare time activities focus more on the music recording industry (audio engineering/production). A frequency-nerd as well, if you will.

    Could I ask how the dynamic factor of 1.3 was determined? This way I can cite a reference in my thesis.

    I'm rounding up my research atm. I've made several possible theoretical suggestions - the one a bit more practical than the other - for an additional overload protection for deckcranes that have not yet been equipped with a heave compensation or load monitor system.
    It would've been nice to know whether HEILA performs retrofits of their load moment indicators/limiters (like the one on the left http://www.heila.com/_imgnews/IMG_9853.JPG [Broken]) on older models, and to have worked more closely with them - since their cranes are a nice bit of technology - but I'm just going to suggest in my recommendations that anyone who wishes to improve their crane work together with the crane corresponding company to work out a practical solution. It's their crane, they 've got all the properties worked out. Seems weird to do it any other way to me.
    Now, most of my calculations have been based on structural hypotheses, due to lack of specifics. Even the response amplitude operator of the ship, to calculate the size of the accelerating forces on the crane, had to be an approximation in the end. They should be in the ballpark however, but still :)
     
    Last edited by a moderator: May 5, 2017
  13. Jul 12, 2012 #12
    Hi,

    I came across this post while looking for some calculation info for flow rates in AHC. I work for a large company involved in subsea activities and look after the cranes on board our fleet.

    I will see if i can dig out some information on boom loadings etc but here are a few things which will help you.

    1. AHC is carried out in two ways on cranes, either directly controling the rotation of the hoist winch or by having a travelling sheave activated by cylinders, they NEVER move the boom to control the location of the load, the main reason for this is the regulations surrounding the luffing (Boom height control) cylinders and their ability to lock in an emergency, the locking mechanisms are not compatible with the flow rates and control necessary for AHC. The choice between cylidner and winch control generally depends on available space, you will generally find large cranes (100T plus) will use cylinders and smaller cranes will operate the winch which is more efficient and puts less load through the system but is more power hungry.

    2. AHC is pretty much only ever used on offshore and subsea cranes as its function is to keep the load stationary when the vessel is moving up and down, read through the DNV regulations and follow the rules for 'Offshore Cranes and Subsea Cranes'.

    3. Even we cannot get any loadings out of the crane manufacturers, it is nigh on impossible and we have to model lots of things ourselves to carry out dynamic simulations. I would base your calculations on the majority of steel being S355J2 grade. If the crane you are looking at has a winch on the pedestal at the rear then the load in the boom can be calculated from line load with a guessed cross sectional area of the boom at the corresponsing angles.

    4. The actual line load should never be more than the SWL of the crane, the dynamic factors are not in addition to the SWL they effectively reduce the SWL. For instance a 13000KG crane with a dynamic factor of 1.3 would be able to operate at only 10000KG. The interesting part is calculation the additional line load due to acceleration and decelleration in AHC.

    Following the DNV rules should get you quite a long way another good one but a lot harder to find is BS EN 13852-1 & 2 which are the international standard for offshore cranes.

    I hope this helps you, if you need more information just ask.

    Cheers

    Alic
     
  14. Jul 12, 2012 #13
    Forgot to mention my main role is hydraulics engineer so im sure i can help with those schematics if you need it as well :)
     
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