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ABSTRACT A model for prediction of damage to tankers during grounding is presented. The model takes into account the coupling between the external ship dynamics and the local damage process of the hull girder. The model for the local damage is based on a least upper bound solution with kinematic compatibility between all structural members. Friction is taken into account, and it is shown how friction contributes to the horizontal resistance force and the vertical reaction force. The resistance of the structural members is expressed in closed forms thus requiring very little modeling time. The model was validated by small-scale tests and a large-scale test. Application of the theory is illustrated by a study of the grounding damage of a single-hull VLCC. INTRODUCTION The urgent political, social and economic reaction to the grounding of the Exxon Valdez and the promulgation of OPA90 presented the opportune climate to mobilize and impel further research activities in the field of crashworthiness of ships. In the automotive industry, the application of international crashworthiness performance criteria is an established practice, preceded by two decades of research and development by the industry and its regulatory agencies. The philosophy of setting performance criteria derived from fundamental principles of mechanics and the detailed knowledge of structural response during a crash has been a driving force for innovative design in this highly advanced and competitive market. In the maritime industry, however, sufficiently detailed and accurate analytical methods for damage prediction due to grounding have not been developed. The existing methods such as those of Minorsky (1959) and Vaughan (1978) are often gross approximations, lacking detail and accuracy due to simplified assumptions, primitive parameters, and debatable failure criteria. The objective of the current paper is to present the basis of an analytical model for assessment of ship damage due to grounding on hard rock.
- Energy > Oil & Gas > Upstream (1.00)
- Transportation (0.88)
ABSTRACT: The objective of the paper is to assess the local damage of long tubular members and pipes caused by the impact of a rigid mass. The formulation is general and covers a wide range of events: low velocity-large mass impacts, as encountered in collisions; medium velocity impacts caused by dropped objects; and projectile and missile impacts. By making assumptions on the cross-sectional deformed shape of the cylinder, the two-dimensional shell problem was reduced to a one-dimensional problem of a plastic string resting on a rigid-plastic foundation. It was shown that the deformation propagates away from the point of disturbance with a constant plastic wave speed and diminishing amplitude. Calculated were the instantaneous velocity and deflection profiles, the final deformed shape of the shell, and the maximum deflection attainable under impact. A parametric study was performed by changing the mass and velocity of the impacting object over several orders of magnitude. An approximation to the dynamic solution was also obtained by using the static solution of the shell under "knife" loading and comparing the plastic work of the deformation process to the kinetic energy of the impacting mass. This approximation was compared to the dynamic solution and good agreement was shown for a range of masses and impact velocities encountered in offshore applications. Finally, use of the proposed methodology was illustrated by predicting the local damage caused by a drill-collar accidentally falling on one of the brace tubular members of an offshore platform. INTRODUCTION Structural impact is of relatively frequent occurrence in offshore construction, drilling and production activities. Collisions of offshore platforms with supply vessels, for example, can be classified as large mass and low velocity impacts. An intermediate range of impact scenarios is covered by dropped objects hitting parts of the protective or load-carrying structure.
- North America > United States (0.46)
- Europe (0.28)
ABSTRACT: The objective of this paper is to assess the effect of ring stiffeners on the local response of cylindrical shells subjected to large deflections caused by transverse concentrated loads. A new model has been developed to account for the strengthening of the shell in the circumferential direction as the deformation zone spreads away from the load application point: The model is general and can be applied to shells with any type of stiffeners. Strains and rotations were also determined to the dent-affected zone near the stiffeners. It was found that ring stiffened shells are more susceptible to fracture than similar shells with uniform thickness. INTRODUCTION The objective of this study is to extend the plastic analysis of local denting of unstiffened cylindrical shells developed by Wierzbicki and Suh (1987) to ring stiffened shells. Observations show that, while the ring stiffeners increase the strength of the shell, they may cause premature fracture in the case of extreme loads. The fracture process is driven by the local stress and strain fields, and these local fields depend on the global deformations and forces in the structure. Therefore, it is important to formulate and analyze the global denting response of the stiffened shell. The present analysis can also be applied in damage assessment of offshore installations collided into by supply boats or moving ice floes; hydrodynamic wave impact on tubular members; impact caused by accidentally dropped objects; and ice scouring of Arctic pipelines. There has been increasing concern in the area of collision and damage of these structures. The approach taken in this research is based on the methodology developed by Wierzbicki and Suh (1987), which analyzed the problem of large plastic deformation of an un stiffened tube subjected to lateral concentrated load, axial force, and bending moment.