I think I can help you. Boundary conditions are those values which are various forces, moments, etc., For the robot swimming, the possible boundary conditions can be the water velocity (upstream or downstream or in still water (v=0 m/s)), temperature, pressure of water, angular velocity of robot hand (for swimming), gravity acceleration (9.81 m/s2), weight of the robot. As far as I concerned these are boundary conditions and these conditions have some other forms like the parameters (velocity,pressure etc.,) can vary with time (in sine or defined wave form) or may be user defined functions (in the form of code with equation describing the movement or parameters).
I think you want do analysis in the CFD for understanding the robot components' resistance. In this case we don't do just CFD analysis on solid components. Of course that the fluid flow in some cases such as aircraft is so important but, this type of loads bring the cracks and/or other phenomena. The parameters that Ananth told are important. But maybe you are searching in FSI simulations that are mentioned in my message. that for structural simulation you should consider other boundary conditions.