26 February 2009

(1991) Huss - Combined Wave Induced Stresses in Ships

Mikael Huss, Combined Wave Induced Stresses in Ships - Application of a rationally based direct calculation method, Report TRITA/SKP-91/1070 (1991) ISSN 0349-0025



Combined Wave Induced Stresses in Ships - Application of a rationally based direct calculation method
Mikael Huss, [Royal Institute of Technology Department of Naval Architecture S-100 44 Stockholm]

ABSTRACT
Calculations of combined wave induced stresses in longitudinal and transverse primary members of ship structures have been performed with a direct method. The wave loads are calculated with linear strip-theory and include global hull girder moments and shear forces, and local loads from external hydrodynamic pressure and internal inertia forces from the cargo. Structural response is calculated by ordinary hull beam idealization for global loads and finite-element analysis for local loads. Results from the linear structural analysis are coupled to wave loads with discrete influence coefficients. Transfer functions of combined stress response in regular waves are obtained by superposition of the different wave induced stress components considering their phase lag. Non-linear stress response from hydrodynamic pressure fluctuation close to the still-water line is evaluated by a simplified time step procedure where the ship motions and global loads are assumed to be linear. Short-term and long-term linear stress responses are calculated for standard wave energy spectra and wave statistics for the North Atlantic.
The statistical correlation between different stress components is analysed and shown to be important to take into account at the design stage. Of special importance is the counteracting effect of external hydrodynamic pressure and internal mass forces in full cargo holds.
The influence of different load conditions, speed reduction, and non-linear effects on the long-term stress distribution is discussed.
Fatigue analysis of a few typical hot-spots are performed considering local geometric stress concentrations and the correlation between nominal normal and shear stresses.
The direct calculation method is found to yield reasonable results and could be advantageous to introduce in the design process especially for novel type of ship structures and for highly optimized structures where the specific ship characteristics must be considered.

KEYWORDS
ship structural design, wave loads, stress response,direct analysis,long-term distribution, fatigue


Contents:

Summary:
Introduction
A Direct Calculation Method
Summary of Results
Some Notes on Long-Term Stress Distributions
Application in an Ordinary Design Process
Conclusions
Acknowledgements
References

Part 1 (1987):
Combined Wave Induced Stresses in a Lo/Lo Containership;
Application of a Rationally Based Direct Calculation Method

Part 2 (1990):
Combined Wave Induced Stresses in an OBO Carrier;
Application of a Rationally Based Direct Calculation Method

Part 3 (1990) :
Prediction of Combined Long-Term Wave Induced Stresses and Corresponding Fatigue Damage in a Ship's Bottom Girder;
Application of a Rationally Based Direct Calculation Method (with Gustaf Lidvall)

Source : mhuss.se

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Summary
Part 1
Part 2
Part 3
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