Comparison and Sensitivity Investigations of a CALM and SALM Type Mooring System for Wave Energy Converters

Abstract

A quasi-static analysis and sensitivity investigation of two different mooring configurations-a single anchor leg mooring (SALM) and a three-legged catenary anchor leg system (CALM)-is presented. The analysis aims to indicate what can be expected in terms of requirements for the mooring system size and stiffness. The two mooring systems were designed for the same reference load case, corresponding to a horizontal design load at the wave energy converter (WEC) of 2000 kN and a water depth of 30 m. This reference scenario seems to be representative for large WECs operating in intermediate water depths, such as Weptos, Wave Dragon and many others, including reasonable design safety factors. Around this reference scenario, the main influential parameters were modified in order to investigate their impact on the specifications of the mooring system, e.g. the water depth, the horizontal design load, and a mooring design parameter.

Reliability Analysis of Single Point Mooring (SPM) System under Different Environmental Conditions

“…In this paper, firstly, the environmental forces (wave & current) were introduced into the flotation control system based on the characteristics of the mooring line under these forces. Then, the probability of failure of each mooring line was studied using these forces [1]. In this paper, firstly, the type and characteristics of the mooring line of SPM is described and secondly the theory of reliability calculation is explained.…”

Experimental Testing and Evaluation of WECs

“…Fig. 9.17 Example of the force displacement-curves and stiffness relative to displacement curves for a catenary and tension leg mooring system [20] Note that the surge excursion of the WEC will be strongly affected by wave groups, even more than from one large individual wave. It is therefore important to repeat the same design wave conditions with different wave trains.…”

Mooring Design for WECs

“…For illustrative purposes a mooring configurations will be used as presented by Pecher et al [14]: a three-leg Catenary Anchor Leg Mooring system, CALM, see Fig. 7.13.…”

“…• Mean wind speed is taken from • Water depth is taken as h d = 30 m from Pecher et al [14] 7.3 Estimation of Environmental Forces…”

“…7.13 Sketch of a three-leg Catenary Anchor Leg Mooring (CALM). [14] The CALM system is composed of three chain-mooring legs directly fastened to the example buoy. This is different to the example by Pecher et al [14] who have assumed that the mooring legs are connected to a mooring buoy, which in turn is coupled by a hawser to a wave-energy device.…”