Posted Chapters of Bjørn Haugen’s 1994 Thesis - PowerPoint PPT Presentation

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Posted Chapters of Bjørn Haugen’s 1994 Thesis

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  1. Posted Chapters of Bjørn Haugen’s 1994 Thesis Title: Buckling and Stability Problems for Thin Shell Structures Using High Performance Finite Elements AFEM Ch 31 - Thesis Ch 4: Triangular ANDES Shell Element AFEM Ch 32 - Thesis Ch 5: Quad ANDES Shell Element AFEM Ch 33 - Thesis Ch 6-8: Numerical Examples and References Complete Thesis (in PDF) available on request

  2. ADMOS 2003, Göteborg, Sweden A New Sandwich Design Concept for Ships Pål G. Bergan Det Norske Veritas, Høvik, Norway and NTNU, Trondheim, Norway

  3. Topics of the Lecture • Some examples of challenges in ship modelling and simulation • Some general problems • Container ship • Liquid natural gas ship • A new concept for building ships using steel and light-weight concrete design • Some conclusions

  4. Characteristics of Ship Structures • “Many pieces of steel welded together”, e.g. more than 100 000 in a large ship • Many types of structural elements: • Outer skins, internal skins • Bulkheads • Integrated ballast tanks • Girders, frames, stringers • Stiffeners, brackets, lug-plates, cut-outs • Cutouts, surface grinding and polishing • Numerous stress concentrations • Corrosion serious problem

  5. Particular Considerations for Modeling and Analysis • Enormous scale effects from overall ship beam (e.g. more than 400 meters long) to stress concentrations around weld or crack • Good modeling of ship beam requires inclusion of a significant number of secondary and tertiary structural elements • Fatigue and fracture analysis requires and detailed and accurate analysis of stress concentrations and cracks • Dynamic response analysis integrated with hydrodynamic simulation • Ultimate strength analysis by way of buckling and/or nonlinear simulation

  6. Wave load analysis Typical Analysis Steps for Ship Analysis

  7. Container ship • Global structural model • 3-and 4-node elements • Containers with low E-modulus • Modelled in PATRAN/NASTRAN, transferred to SESAM

  8. Hydrodynamic Model

  9. Hydrodynamic Load Analysis Dynamic pressures for head sea and max hogging condition

  10. Ultimate load state (ULS) checks

  11. Hot spot stress analysis at hatch corner

  12. Liquid Natural Gas (LNG) Ship Global finite element model

  13. Stepwise Construction of Global Model

  14. Wave Motion and Pressures

  15. Hot Spots

  16. Structural Problems: Bulk Carrier

  17. Steel – Light-weight Concrete Sandwich From complex steel structure to clean sandwich structure The main idea is to replace stiffened steel panels by steel-concrete sandwich elements for main load carrying structural components

  18. Cellular Sandwich The light-weight concrete is filled into the space between the surface steel sheets to completely occupy the internal space and bond to the steel along all sides • The steel sheets provide the major part of the structural strength • The concrete provides some strength and stiffness in compression, but not in tension (conservative assumption) • The concrete provides a stiff spacing between the surface sheets and supports against surface skin buckling • The need for secondary stiffeners is eliminated • The concrete has sufficient strength to transfer relevant transverse shear forces in plates • The number of details prone to coating failure with subsequent corrosion and fatigue is greatly reduced • A concrete with a density below approximately 900 kg/m3 is preferred to keep down the total weight Steel plate Light weight aggregate concrete Steel plate Thin walled steel spar box

  19. Using Experience from Other Applications • Steel-concrete sandwich elements have been used successfully for bridge structures, which are also exposed to large dynamic loads and demanding environmental conditions • Composite sandwich structural elements are used in air plane wing structures, wind turbine wings, trains, naval ships, and other severely loaded structures – as a particularly efficient design solution • Shipbuilding should learn from successful experiences in other industries

  20. Panmax Bulk Carrier

  21. Some Characteristics of the Concept • Longitudinal girder stiffened double bottom structure • Solid sandwich structure in deck • Continuous hatch coaming beam structure • Partly hollow sandwich elements in ship sides, transverse bulkheads, and double bottom • Traditional fore and aft ship design in the present study • Ballast water carried primarily in cargo holds • HT 36 steel throughout cargo area • Minimum steel skin plate thickness 10 millimetre • Concrete properties (example) • density 900 kg/m3 • compressive cube strength 14 MPa • tensile splitting strength 2.5 MPa • failure strain in compression 2-2.5 ‰ – similar to yield strain for steel • E-modulus 6000 MPa • More than 50 % of concrete strength achieved after a few days

  22. Cross-section of ship beam • Global and local load cases from DNV Steel Ship Rules • Initial scantlings selected • Linear FEM analysis to determine sectional forces – with stiffness contribution of concrete in both compression and tension • Scantling optimisation of sections assuming no tensile concrete strength – safety factor 1.4 for concrete compressive strength • DNV Steel Ship Rule longitudinal strength requirements satisfied without including contribution from concrete • Confirmation that all local buckling modes are eliminated • Depth of sandwich minimum 70 millimetre to avoid global buckling of deck slab outside the hatch coaming

  23. LNG carrier Primary barrier 9% Ni Steel or Invar steel Insulation layer e.g. geomaterial

  24. LNG carrier

  25. Tanker for oil or chemicals Sandwich deck Easy to clean ballast cells Ice strengthened side structure Stainless steel primary barrier

  26. Safety and Structural Attributes • Reduced number of fatigue and corrosion prone details • Buckling failure modes virtually eliminated • Increased hull torsion stiffness • Increased energy absorption in case of collision or grounding • Increased strength to withstand explosions and accidental loads • Increased stiffness of aft ship to avoid vibrations and propeller shaft bearing damages

  27. Safety and Operational Attributes • Increased resistance against damage from cargo handling equipment • Better damping of dynamic stresses and response from hydrodynamic loads • Enhanced damping of noise and vibrations from machinery and propulsion system • Simplified hull structure maintenance • Significantly reduced coating area • Increased service life • Highly fire resistant and insulating hull