SUMMARY:

Application of the modern ship structural design procedure is presented on the mega yacht example for all design phases (concept, preliminary and detail). Benefits of utilization of modern rational design support technique (FEM, optimization, etc.) are demonstrated through achieved results (reduction of weight/cost and increase of safety). Approach which employes full ship FEM model which enables simulation of the realistic 3D effects without restricting assumptions proved to be the right choice. Presented work is a result of the successful cooperation trough joint work of industry and FSB research teams and represents an example of modern procedure in structural design of complex ships.

SAŽETAK :

Primjena moderne procedure projektiranja konstrukcije broda prikazana je na primjeru mega jahte za sve faze projektiranja (konceptualna, preliminarna i detaljna). Prednosti primjene modernog i racionalnog pristupa podršci projektiranju (optimizacija, MKE, itd.) demonstrirane su kroz dobivene rezultate (smanjenje mase i cijene te povećanje sigurnosti). Prisup zasnovan na primjeni MKE modela cijelog broda koji omogućava simulaciju realističnih 3D efekata bez ograničavajućih predpostavki pokazao se kao pravilan izbor. Prikazani rad predstavlja rezultat uspješne suradnje kroz združeni rad industrijskog i FSB istraživačkog tima te predstavlja primjer moderne procedure projektiranja konstrukcije složenih brodova.

Industrial project with VEGAYACHTS and Rolls Royce Marine

AS Merchant Solutions 2011 - 2012

MEGA YACHT (Loa = 100.8 m) Based on the general arrangement plan developed by VEGAYACHTS (VY) and the initial structural design made by Rolls Royce Marine AS Merchant Solutions (RRM), structural optimization and direct calculation analysis of the mega yacht were performed by FSB. Direct application of structural support techniques during all phases of design was performed with the following goals: reduction of the structural weight, VCG position and vibrations with simultaneous increase of overall structural safety. Structural design was made on the basis of Lloyd Register’s (LR) Rules for passenger ships.

Concept design phase: Objectives were to evaluate global strength and contribution of the superstructure to structural resistance to hull girder loads, cross sectional stress distribution along the ship length, transverse structure stress distribution due to racking and force distributions in pillars.

Fig.1 General Arrangement - Profile (design by VY and RRM).

Two mega yacht full ship coarse mesh FEM models of different length with the variable web frame spacings in the superstructure and different framing of the double bottom structure were optimized regarding weight of steel structure using MAESTRO and DeMak optimization framework extended trough PhD Thesis (Prebeg 2011). Property based element group approach was developed (Žanić, Pirić 2011) and used in the optimization process. Efficient optimal solutions were generated for the selection of the preferred design variables. Optimal solutions ranged in mass per length change 30.1 - 21.9 t/m, where all respective safety values were increased.

Fig.2 Vertical displacements for load case LC3 - Max. Hogging.

Fig.3 History of weight/safety changes through design cycles.

Full ship scantlings Weight[t] / savings VCG [mm]

Prototype SPL,D Steel self weight 2129 0 6875 0

Light ship 4123 0 7360 0

Proposed Ship Design SDL,D

Steel self weight 1878 -251 7647 772 Light ship 3872 -251 7782 422

Fig.4 Comparison of Prototype and corresponding Optimized Design.

Preliminary design phase: Main structural scantlings of the preferred mega yacht model determined in concept design were verified on more refined full ship FEM model. Global hull girder and substructure free vibration calculations (dry/wet) using full ship FEM model were performed to verify acceptance of vibration criteria, as a first step towards forced vibration calculations. Comparision of results obtained by eigenvalue solver developed by PMF (Grubišić 2011) and MAESTRO and NASTRAN solvers was performed.

Detail design phase: Trough cooperation with SME Bonum d.o.o., FEM model from the preliminary design phase was refined on fine mesh level to suit LR requirements for verification of critical structural details: large side screens, windows and other large side openings, hull to arc structure connection, critical details in the aft ship structure, etc.

Fig.6b Substructures free vibration f=15.02Hz-1V Upper deck.

Fig.5 Global hull girder free vibrations

(wet mode), f=2.73Hz - 1V.

Fig.7 Evaluation and redesign of critical structural details.

Fig.6a Substructures free vibration f=15.86Hz-1V Main deck.

Zavod za brodogradnju i pomorsku tehniku, Katedra za konstrukciju plovnih objekata

Department of Naval Architecture and Offshore Engineering, Chair of Ship Structures

OCTOPUS GRUPA – ISTRAŽIVAČKI RAD UZ PODRŠKU PROJEKTANTIMA NA SLOŽENIM PROJEKTIMA

OCTOPUS GROUP – RESEARCH SUPPORTING HIGH LEVEL CONSULTING

www.fsb.unizg.hr/octopus/ | V. Žanić, (Mentor/ Project leader) | Collaborators: J. Andrić (Structural design of multi-deck ship); P. Prebeg (Optimization); M. Grgić (Slamming loads); K. Pirić (Reliability based design); M. Stipčević (Design loads).