Q2. What is the purpose of the present simulations?
In the present simulations, the sharp edges of the wave energy converter are to play a very important role in generating vortices, which in turn would influence the total viscous drag force(s).
Q3. What was the boundary condition applied to the CFD wave tank?
To minimize wave reflection from the downstream (right hand side) end of the wave tank, the outflow boundary condition was applied together with stretched cells adjacent to this boundary.
Q4. What is the frequency step used in the discretization of the spectrum?
Df being the frequency step used in the discretization of the spectrum S. And i being the index of the frequency (or angular frequency) of the waves.
Q5. What is the reason for the high frequency noise on the in-line force curve?
It seems that for relatively large KC value the surrounding fluid becomes more turbulent and coupling of the low pressure vortex formation and the possible reflection from the outer boundaries appear to be as a major reason for the high frequency noise on the in-line force curve.
Q6. What is the optimum mesh structure used in all simulations?
As discussed in [34], wave height attenuation can occur in CFD simulations therefore the optimum mesh structure employed in all simulations insured that the desired wave achieved at the device location is within a reasonable accuracy.
Q7. What is the effect of the addition of the viscous drag on the device displacement?
Looking at the device displacement with and without the drag term at time instants of 20 s and 30 s, it can be noted that the addition of the viscous drag not only reduces the extent of the over-estimation of the device motion but also introduces nonlinearity in the resultant motion like the one shown by CFD simulations.
Q8. What is the reason why the inertia coefficient of this scenario is usually written as?
It has been mentioned that when the fluid is oscillating while the cylinder is at rest, the inertia force is increased by the Froude–Krylov force caused by the pressure gradient and this is the reason why the inertia coefficient of this scenario is usually written as Cm ¼ Ci þ 1.
Q9. How is the PTDV model compared with the CFD?
when the drag force corresponding to the nominal value of the Cd is included into the PTDV model the comparison with the CFD is reasonably quite good for the first 30 s of wave structure interaction.
Q10. What are the advantages of using CFD?
CFD results have been presented along side existing experimental data and the advantages of using CFD, such as the ability of readily jump to various scale models and quick assessment of the design variables, are highlighted.
Q11. What is the average drag coefficient for a cylinder with round corners?
In [26] numerical results for oscillatory flow past a cylinder with round and with sharp corners are presented and an average value for the drag coefficient is reported to be around 2.9.
Q12. What is the relative velocity of the float with respect to the velocity of the waves?
It is worth noticing that Ur is the relative velocity of the float with respect to the velocity of the incoming waves, that is Ur ¼ _X V , where _X is the instantaneous velocity of the buoy as it moves in response to the waves and V is the corresponding incoming wave velocity taken in accordance to the linear wave theory for deep water scenario.
Q13. What is the difference between the drag force and radiation force?
Although for this specific case of small amplitude linear monochromatic wave, the drag force is relatively small as compared to the radiation force and therefore the corresponding sum of the drag force and the radiation force offers only a slight increment and is able to capture the peak of force curve as observed in the CFD model.