Abstract
Previous research has indicated that the fluid-structure interactions of slender members in offshore structures are extremely sensitive to the ratio of wave frequency to the natural frequency of the structure, ƒw/ƒNw. This paper presents experimental measurements of forces and response displacements from a spring-mounted vertical cylinder in regular waves for a constant surface Keulegan-Carpenter number, SKC, equal to 8 and frequency ratios in the range 0·3≤ ƒw/ƒNw≤0·8. Peak values of force coefficients and response amplitudes are observed to occur when the frequency ratio f. If,. is an integer submultiple. Further peaks may also occur for ƒw/ƒNw =1/[(SKC/2π) + 1] and ƒw/ƒNw =1/[(SKC/2π) + 2] due to coupling between the in-line force and transverse response. Reasonable agreement is found between the experimental resonant force and response displacement loci with a simulation based on a finite-difference time-stepping solution of the non-linear equations of motion.
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