Feature 2 | FINLAND’S MARINE INDUSTRIES VTT remains leading light
Among the recent stand-out research projects at VTT are a new passenger vibration analysis and new work on fracture mechanics procedures.
Technical Research Centre of Finland has developed its own methods for global vibration analysis of passenger vessels. Seppo Kivimaa, technology manager at
A
the Vehicle Engineering unit at VTT told Te Naval Architect that the research had included numerical calculations, model tests and full scale measurements of wave loads and hull response at sea. Typically, for the dynamic analysis of a complicated construction, such as passenger ship’s hull, a 3-D finite element model of the hull is made first, including necessary structures and masses. Ten the natural frequencies and modes are calculated. Te calculation of vibration response
for harmonic impulses, such as those from propellers, is rather straightforward. However, there are still challenging areas of study, including the modelling of the added mass caused by the surrounding water in free vibration, or the calculation of hull vibrations for wave impact loads. VTT’s solution has been an approach
where impact loads are simulated from model scale pressure measurements, and are fed into the simulation model, including the dynamic characteristics of the hull, over a period of time. VTT has also developed methods to calculate
ſter several years of systematic study on ships’ hull loads and dynamic behaviour, VTT
Fatigue assessment of welded joint in door corner with detected cracks using fracture mechanics and design material data.
and to improve the predictability of the calculation model and structural analysis. Some 10 to 20 transducers are needed to measure and analyse global vibrations on a cruiseship properly. “Te regulations for noise and vibrations induced by the propeller and onboard machinery are clearly specified, but there are no clear norms for the level of vibrations induced by wave impacts. Tis is the area we are focusing on,” Mr Kivimaa said.
Fracture Mechanics The methods and models developed by VTT are also used for strength and fatigue calculations for cruiseships. Te work is done together with owners and shipyards. Mika Bäckström and Mr Kivimaa at
Fatigue assessment of a welded joint in a door corner with detected cracks using fracture mechanics and design material data.
passenger comfort indexes, which are visualized in different colours based on how passengers feel the vibration (see picture below). VTT is systematically gathering full
scale data measured on cruiseships, to verify the accuracy of the calculations,
VTT Vehicle Engineering completed a study on the development and utilisation of fracture mechanics procedures in fatigue life assessment of ship structures. Te work was performed within the scope of the project MARSTRUCT, Network of Excellence on Marine Structures, (www.
mar.ist.utl.pt/marstruct/), which has been financed by the EU through the GROWTH Programme. In general, the fatigue assessment
of ship structures within the rules of classification societies is based on design S-N curves and the Palmgren-Miner’s Rule for consideration of variable amplitude loading. Germanischer Lloyd’s rules refer to the usage of the fracture mechanics in cases where cracks have been already initiated or welds are only partially penetrated. Additional principles of fracture mechanics and different fracture mechanics procedures are used to assess the residual strength and residual life of cracked structures in aircraft,
Passenger comfort index on a recent cruise ship newbuilding. The index is visualized in different colours based on how passengers feel the vibration.
66 The Naval Architect February 2009
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92