Most fatigue loaded structural components are subjected to variable amplitude loads which must be processed into a form that is compatible with design life calculations. Rainflow counting allows individual stress cycles to be identified where they form a closed stress–strain hysteresis loop within a random signal, but inevitably leaves a residue of open data points which must be post-processed. Comparison is made between conventional methods of processing the residue data points, which may be non-conservative, and a more versatile method, presented by Amzallag et al. (1994), which allows transition cycles to be processed accurately.This paper presents an analytical proof of the method presented by Amzallag et al. The impact of residue processing on fatigue calculations is demonstrated through the application and comparison of the different techniques in two case studies using long term, high resolution data sets. The most significance is found when the load process results in a slowly varying mean stress which is not fully accounted for by traditional Rainflow counting methods

The paper looks at the use of blade element-momentum theory for predicting the torque and thrust on a marine current turbine and the results of wave tank tests using a 400 mm-diameter rotor model. To include the effects of waves, linear wave theory particle velocities and accelerations were integrated into the mathematical model. Comparison with test data shows a good agreement which implies that the theory can be effective in analysing the wave-current interactions in marine current turbines. The paper also carried out parametric studies into related parameters, which include wave height, wave frequency, and tip-speed ratio. The interaction of waves with the current may increase or decrease the torque and hence power output of the turbine. The paper also explains the selection and manufacture of the rotor and the experimental setup.