Title Sigurnost konstrukcije spremnika na brodovima za prijevoz ukapljenog plina
Title (english) Safety of cargo tanks on liquefied gas carrier
Author Smiljko Rudan
Mentor Ivo Senjanović (mentor)
Committee member Jurica Sorić (predsjednik povjerenstva)
Committee member Ivo Senjanović (član povjerenstva)
Committee member Većeslav Čorić (član povjerenstva)
Committee member Slobodan Kralj (član povjerenstva)
Committee member Nenad Vulić (član povjerenstva)
Granter University of Zagreb Faculty of Mechanical Engineering and Naval Architecture Zagreb
Defense date and country 2006-05-30, Croatia
Scientific / art field, discipline and subdiscipline TECHNICAL SCIENCES Shipbuilding
Universal decimal classification (UDC ) 629.5 - Watercraft engineering
Abstract Ukapljeni plin jedan je od najvažnijih energenata današnjice. Diljem svijeta transportira se cjevovodima ili ukapljen u spremnicima brodova za prijevoz prirodnog (LNG) ili petrolejskih plinova (LPG). Nezavisni spremnici tipa C, koji ukapljeni plin prevoze pod tlakom i djelomično pothlađen, najčešće su cilindričnog ili dvodijelnog oblika i projektiraju se prema pravilima klasifikacijskih društava. Izostanak iole značajnijeg incidenta u pomorskom prijevozu plina svjedoči o pouzdanosti tih pravila i konstrukcije spremnika. Ipak, relativno jednostavna pravila ne mogu dati detaljan uvid u stvarno ponašanje konstrukcije, niti mogu odgovoriti na specifična praktična pitanja vezana uz osnivanje i gradnju spremnika. Istodobno, spremnici su sve veći i njihova izrada je tehnološki složenija, stalne rute brodova zamjenjuje "čarter" plovidba diljem svijeta, nastoji se osigurati siguran prijevoz plina u djelomično ispunjenima spremnicima ili pod većim tlakom. Sve to ukazuje na potrebu za točnijom analizom i boljim razumijevanjem odziva brodske konstrukcije i spremnika u uvjetima realističnog valnog opterećenja. Istodobno, valja dati odgovore na pitanja iz brodograđevne prakse koja se tiču pouzdanosti konstrukcije spremnika, posebno onih vezanih uz pojavu koncentracije naprezanja u tankim ljuskama, nesavršenosti geometrije uslijed tehnoloških ili drugih ograničenja pri sastavljanju spremnika, te ocjenu ukupne zamorne izdržljivosti posebno opterećenih strukturnih detalja spremnika. U ovom radu prikazane su analitičke i numeričke metode kojima je moguće izravno istražiti i ocijeniti sigurnost konstrukcije spremnika na brodovima za prijevoz ukapljenog plina. Prikazane su osnove teorije tankih rotacijskih ljusaka i približni analitički izrazi za određivanje sila i deformacija u cilindričnoj, konusnoj, sfernoj i torusnoj ljusci. Detaljno je opisana spektralna analiza naprezanja u sva četiri njena koraka: proračun hidrodinamičkog opterećenja, kvazi-statički proračun odziva brodske konstrukcije i određivanje prijenosnih funkcija zareznog naprezanja u vrhu zavara, statistička analiza i dugoročna razdioba naprezanja u funkciji parametara službe broda i izračun visokocikličkog zamornog oštećenja promatranog strukturnog detalja. Opisani postupak detaljno je prikazan kroz primjer u kojem je provedena parametarska spektralna analiza nesavršenog Y-spoja cilindričnih ljuski i uzdužne pregrade dvodijelnog nezavisnog spremnika tipa C na LPG brodu 6500 m3. Različite vrijednosti ekscentriciteta Y-spoja izmjerene su na stvarnom spremniku, gdje uzrokuju pojavu visokih vrijednosti koncentracije naprezanja i prisutnost momenta savijanja u konstrukciji koja se projektira na osnovi membranske teorije. Stoga je provedena analitička i numerička analiza nesavršenog Y-spoja i predložena sanacija tih nesavršenosti. Dalje, prikazani su postojeći postupci određivanja niskocikličkog zamora koji nastaje uslijed punjenja i pražnjenja spremnika, odnosno varijacije tlaka u njima. Proračunom niskocikličke zamorne izdržljivosti Y-spoja za različite vrijednosti ekscentriciteta ilustrirana je primjena metode. Konačno, prikazani su postojeći koncepti određivanja kumulativnog visokocikličkog i niskocikličkog zamora. Vrijednosti koncentracije naprezanja analizirane su analitički i numerički na mjestima spoja cilindrične i torisferične ljuske, te za slučaj nesavršenog spoja limova na čelu spremnika i pojave konusnog spoja malog kuta. Na kraju je istaknut znanstveni doprinos provedenog istraživanja i potvrda rezultata istraživanja kroz praktičnu primjenu rezultata u brodograđevnoj praksi.
Abstract (english) Liquefied gas is one of the most important sources of energy nowadays. Worldwide it is being transported by pipelines or in liquefied state in tanks on Liquefied Natural Gas or Liquefied Petroleum Gas carriers. The independent tanks of type C, which contain liquefied gas both under pressure and refrigerated, are most commonly made in cylindrical or bilobe shape and are designed according to the Rules of classification societies. Absence of any serious incidents in seagoing transport is good evidence of the reliability of these rules and the tank construction itself. However, simple rules may not provide insight into actual behavior of ship and tank construction nor do they provide answer to the specific practical questions arising from the tank design and assembly practice. At the same time the tanks are becoming larger and therefore their constructions is becoming more technologically demanding, the fixed sailing routes are being replaced by the worldwide charter sailing, efforts are made to assure safe transport in the case of partially filled tanks or tanks under higher pressure. These reasons give rise to the need for more accurate analysis and better understanding of ship structure behavior subjected to realistic hydrodynamic loading. At the same time, shipbuilding practice requires answers to open problems of tank structure reliability, particularly related to stress concentration in thin shell structures, imperfection of geometry due to technical and other limitations during the tank assembly process, fatigue strength assessment of critical tank structural details, etc. This thesis presents both analytical and numerical methods for direct calculation of LPG tank structure safety. An overview of the theory of thin shells of revolution is presented and approximate analytical expressions for forces and deformations determination are given for cylindrical, conical, spherical and toroidal shells. A full spectral analysis is described in detail for each of its four steps: the hydrodynamic load calculation, quasi-static analysis of ship structure response, evaluation of notch stress transfer functions at the weld toe, statistical analysis and longterm distribution of notch stress as function of ship sailing condition and the calculation of highcycle fatigue damage for the structural detail under observation. The application of the method is presented through illustrative example: full parametric spectral analysis of imperfect Y-joint of cylindrical shells and longitudinal bulkhead of a bilobe tank in 6500 m3 LPG carrier. Different values of Y-joint eccentricity are found and measured on the existing bilobe tank, leading to high stress concentration and the presence of bending moment in membrane theory designed structure. Therefore, a comprehensive analytical and numerical analysis of Y-joint is performed and remedies for this imperfection are proposed in a systematic manner. Furthermore, low-cycle fatigue analysis methods are presented since low-cycle fatigue governs a significant part of the fatigue life of structural details subjected to tank pressure variation during cargo loading and unloading cycles. The application of the method is illustrated by low-cycle fatigue damage estimation for different values of Y-joint eccentricity. Finally, cumulative high-cycle and lowcycle fatigue damage concepts are presented. The stress concentration has been analyzed both by analytical and numerical methods in the case of cylindrical and hemispherical shells and in the case of imperfect joint of tank dish shells where a small angle conical joint had been formed. In the end, the scientific contribution of the performed research has been pointed out as well as the verification of research results through their practical application in shipbuilding practice.
Keywords
brodovi za prijevoz ukapljenog plina
brodska konstrukcija
nezavisni spremnici
dvodijelni spremnici
opterećenje spremnika
nesavršenost izrade
koncentracija naprezanja
teorija ljusaka
metoda konačnih elemenata
visokociklički zamo
Keywords (english)
liquefied gas carriers
ship structure
independent tanks
bilobe tanks
tank load
misalignment
stress concentration
thin shell theory
finite element method
high-cycle fatigue
low-cycle fatigue
spectral analysis
Language croatian
URN:NBN urn:nbn:hr:235:513707
Study programme Title: Mechanical Engineering and Naval Architecture Study programme type: university Study level: postgraduate Academic / professional title: doktor/doktorica znanosti, područje tehničkih znanosti (doktor/doktorica znanosti, područje tehničkih znanosti)
Type of resource Text
File origin Born digital
Access conditions Open access
Terms of use
Created on 2020-12-28 13:33:33