Application of Wide Band Spectrum of Large Container Ship's Fatigue Analysis
- Beom-il Kim (Ship & Plant Technology Center, Korean Register of shipping Busan) | Sun-kee Seo (Hull Rule Development Team, Korean Register of shipping Busan)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- Fatigue Damage, Large Container ship, Springing effect, Fluid-structure interaction, Wide band spectrum
- 1 in the last 30 days
- 13 since 2007
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In case of containerships with large open deck structure, which make a wide band random response when the natural period of the incoming waves meet that of the ship. This phenomenon is called springing. This is related to fatigue damage of the ship and many researches have been carried out by coupling fluid - structure in order to predict fatigue damage. In this study, in order to predict the fatigue damage of large container ship under wide band random loads, the fatigue analysis was performed based on modal superposition approach. The calculated stress RAO was applied to several representative wide band spectrum and spring effect was analyzed based on spectral method.
As the world marine transportation increases, the recently built container ships tend to have a larger size and a faster ship speed. Accordingly, the natural frequency of hull increases and intersects with the natural frequency of wave due to the increase of ship speed. Such intersection generates separate high energy in the range of response frequency, which exceeds the frequency band with high energy. Hull hydro-elasticity response, which is represented by springing and whipping, is call wave induced vibration, and has the natural frequency of hull, unlike wave induced load. Response-induced structural vibration occurs intensively in a particular condition. If this phenomenon is not considered in design phase, the hull structure may undergo unexpected damage and even destruction. For this reason, the demand of ship’s owner for relevant analysis is drastically increasing.
The analysis of the hydro-elasticity response of ship started from the late 1970s. Most of the studies were based on modal superposition. And, instead of analyzing a three dimensional structural model, a ship was idealized by beam elements along the longitudinal direction, and Euler beam or Timoshenko beam theory was applied to analyze the hydro-elasticity response of the ship. Many studies have been performed to overcome the inefficiency of using the 3D model and to examine the strength at the initial stage of the design. Bishop et al. (1985) performed dynamic calculations using beam theory such as Euler-Bernoulli, Timoshenko and Vlasov in order to analyze the behavior of the open- thin structure and comparing with experimental results on uniform cross section beams, Timoshenko and Vlasov beam theory proved relatively good results. Wu and Ho (1987) modeled the transverse bending -torsional interaction behavior of a ship with open section as a one -dimensional beam element considering warping deformation and calculated the dynamic response by wave loading. Senjanovic et al. (2006, 2009) developed a one-dimensional beam element that takes into account the effects of warping deformation and intramembrane shear deformation, and applied it to the calculation of the elastic properties of pontoons and large container ships. Lee et al. (2006) and Lee et al. (2003) attempted to analyze the elasticity problem of a ship by applying the Timoshenko beam theory and the Euler beam theory in the frequency domain using the three-dimensional source method. Kim. et.al (2010) analyzed the torsional behavior of a large container ship under oblique sea conditions by combining finite element method (FEM) based on one-dimensional beam element and high-order boundary element method (BEM) based on the Rankin panel.
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