More research is needed to better characterise rope tensile properties, and provide ways in which rope test schedules can give mooring analysts the necessary stiffness data in a useful form. In addition, ropes as made undergo an irreversible elongation, known as bedding-in, during initial loading cycles due to tighter packing and local adjustments of length differences of the fibres, yarns and strands. For organic fibres, as described in Sections 2.5.3–2.5.5 2.5.3 2.5.4 2.5.5, stress is a multi-valued nonlinear function of strain, which depends on the total time-dependent prior history and the current deformation conditions. Provided the plastic limit is not exceeded, stress in steel is a single-valued, linear function of strain. O'Hear, in Handbook of Fibre Rope Technology, 2004 12.3.3 Rope stiffnessįibre ropes introduce a new feature, which is not commonly met in structural engineering. In reality, there might be a phase difference between incident wave and response, but we are neglecting it here for simplicity. For example, for an incident wave with amplitude a i, the response of motion η j will be H ( ω ) a i. Physically, H ( ω i ) is the response per unit wave amplitude at WF ω i. Here η can also be replaced by any other term such as wave drift force once the basic assumption of linearization is satisfied such that the response can be superimposed with different frequency components.
To look at this concept in more detail, let us denote H ( ω ) as the response transfer function for motion η. A response transfer function builds a bridge connecting incident wave spectrum in WF analysis or wind spectrum in LF calculation to the response spectrum of our interest. Yongyan Wu, in Mooring System Engineering for Offshore Structures, 2019 5.5.1 Response transfer functionsīoth WF and LF mooring analysis involve a vital concept called the response transfer function.