Experimental Study on Hydrodynamic Forces Acting on the Oscillating Rectangular Cylinders

Abstract

This study aims at making clear of the advantageous performance of the rectangular cylinder over the circular one as the lower hull of the offshore floating structure. This paper presents the results of the experiments for the hydrodynamic forces acting on the oscillating rectangular cylinders. Tests were carried out on the cylinders having cross-sectional aspect-ratio 0.1 to 0.8. Results are presented for each cylinder as added mass coefficient C_a and damping coefficient C_d. These coefficients are correlated with the amplitude ratio πa/b. When the added mass and damping coefficients of the rectangular cylinders are compared with those of the plate and cylinder obtained by Keulegan et al, the following conclusions are derived; 1) When the aspect-ratio d/B equals to 0.1 or 0.2, the hydrodynamic coefficients C_a and C_d agree with those of flat plate. 2) As d/B becomes greater than about 0.4, C_d reduces nearly half of flat plate at the moderate amplitude ratio. However, C_a shows a constant tendency. 3) Comparing with the coefficients of the circular cylinder, both C_d and C_a are considerably great. Therefore, it can be seen that the rectangular cylinder yields the greater resistance against the exciting oscillations than the circular cylinder.