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This paper presents a numerical model, based on the displacement of one point of the material flow relative to a fixed reference point, in order to formulate the heat generation during friction stir process and thereby calculate the temperature difference between advancing and retreating sides. This model considers frictional heating dependent on both the temperature and the velocity of the tool, as well as heat generation due to plastic deformation dependent on temperature, and assumes that friction heat at high temperature was replaced by heat generation due to plastic deformation. The heat generated by plastic strain energy dissipation in thermomechanically affected zone is calculated by a new technique, and the convection heat transfer coefficient and the sticking state parameter are considered as a function of temperature. Finally, the thermal equations are solved using a nonlinear finite element code ABAQUS. The numerical results correctly showed the asymmetric nature of temperature distributed at different sides of the weld line which have good agreement with experimental data that are presented in the literature.

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This article presents the novel hybrid Wavestar–Hywind concept that combines a floating wind turbine with a number of Wavestar point-absorbers on a shared OC3-Hywind spar platform. The effect of increasing Wavestar number on the wave power production and platform motions has been investigated using both time and frequency domains. Simulations were carried out with the boundary element method using the three-dimensional diffraction/radiation theory, which is employed by the ANSYS AQWA software. Regular Airy wave under different wave periods from 4 to 16 s and constant wave height (1.2 m) was considered as an environmental condition. The results of the response amplitude operator (RAO) motions of the platform show that increasing wave periods cause an increase on the surge, heave, and pitch RAO. Moreover, in higher periods as Wavestar numbers increase, the heave motion decreases, while it does not significantly affect the surge and pitch motions. Due to Wavestar resonance, the maximum capture width ratio occurs in wave periods 5 and 6 s for all case studies, that means higher Wavestar power and lower platform motion due to increasing radiation damping force. Furthermore, the result shows that the angle between Wavestar arm and wave direction and its location are two main factors that influence the power production. The maximum power absorbed by Wavestar occurs in the wave periods 6 s and makes 46, 103, 160, and 210 kW power for 3, 6, 9, and 12 WS, respectively.

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