Ship grounding or ship collision with an underwater obstacle is a frequent event when navigating in offshore waters. Consequences may be disastrous to the environment when oil spilling occurs. Now a ban for single bottom tankers to navigate in busy Baltic Sea, especially in winter, is considered as a legal measure to prevent such occurrence. Development of grounding (collision) forces and their effect onto navigation of the double bottom ship is studied in actual research. As a result of collision or grounding ship hull may be damaged getting a dent or tearing along hull plating. Anyway, a kind of geometrical penetration of the obstacle into initially undamaged hull surface occurs. This penetration produces a certain force that, depending on its magnitude, changes ship position and motion. Constitutive relation between geometrical penetration and resulting force is established by FE method when meshed section of a double bottom ship is subjected to penetration of a rigid obstacle with certain constant velocity, very low to avoid inertia effect. Buckling of thin walled hull structures and non-linear effects, such as plastic deformations, non-linear material behaviour and geometric non-linearity, are taken into account. Contact explicit formulation is used for this part of analysis. According to constitutive relation the grounding normal and tangential forces are evaluated. Computed forces and ship movements are compared to experimental results coming from ship model tank tests.
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