When fragments entering water at high speed, velocity attenuation coefficients of the fragments calculated by different scholars were quite different. Through theoretical analysis and numerical simulation, the velocity attenuation characteristics of the fragments with different head shapes, water entry angles and aspect ratios are studied in this paper. Numerical results show that for the fragments with different head shapes, the main factors affecting the velocity attenuation of the fragments are different. In particular, the influences of the pier’s rough effect on the velocity attenuation of the cylindrical fragments (aspect ratio ≥ 0.5) and pie fragments (aspect ratio < 0.5) are different. As the water entry angle is decreased, the fragment velocity attenuation is slowed down by the “deflection effect” of the fragment. Considering the reduction of drag coefficient, a modified velocity attenuation formula is presented for the pie fragments during high-speed water entry.

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