3-dimensional flow simulation for the design of the optimized parameter of surfing board
The Grid Size of flow field which is modelled in Figure is 41 * 101 * 41 in x, y, z axis each.
The depth of board which is under the water is 0.1 meter because we designed the thickness of board as 0.2 meter. Although the width of board is designed
as 0.5 meter, the width of real board is more narrow tnan the designed board. When a researcher is modelling the flow field around a board, he need to
supplement the length, width and depth of surfing board.All of the cross sections in the direction of the width of the board ie, in the direction of the x axis are designed as an arc of circle. We must refer to real board and design sketch in order to know whether the cross section of the real board is the same with this form. We haver to consult with the designer of the surfing board because the cross sectional shape in the direction of y axis and the shape of the curved surface of the bottom is not identified by an external appearance.
In CFD anslysis of a board, we cosider both the atomospheric pressure Pa at the surface of
the water and head pressure rgh which is changed in accordence with the depth due to the weight of water, together. In the initial condition of flow field,
the boundary condition of pressure is changed in the direction of the depth of water ie. in the direction of the z axis, and the equation should be P = P + rgh
where h is changed with z axis. We decided the velocity of board which is move towoard the front as 5 m/sec.
In this analysis, the strength of lift which is primary design goal, is the sum of the buoyancy force which is produced
by the specific gravity of the board and the lift which is produced by the flow field which is formed for the board
to go ahead. So, if the strength of the lift is bigger than the sum of the weight of the standard boarder whose weight is 60Kg and
the weight of the board then the surfing board is still swimming and will not go down.
Although we analyze the simulation result of the surfing board, generally streamline shaped object is moving
in the fluid at fast velocity, then the vortex shaped secondary flow is occurring around the board. Because the cross section of board is covex arc shape, clealy the
vortex shaped secondary flow which moves from the inner part of the board to the outer part of the board will be formed. If the flow go down from the center of the board
to the outer part, this is a phenomemnon caused by high pressure field, and the lift force is occurred in the surfing board. Parameter Control for Optimized Design of Surfing Board
- First of all we modelled two boards which have a different width each other in order to know optimized design value of the boards. One board haver the width of 0.7 meter and the other board have the width of 0.35 meter and we try to test the lift characteristics in the water which have the same desity.
Width : 0.35 m Depth in the water : 0.1 m
DR : 0.2 m
LR : 6 m
LRC : 7.1 m
Width : 0.7 m Depth in the water : 0.1 m
DR : 0.5 m
LR : 6 m
LRC : 7.4 m
Basic Consideration about Surfing Board
The surfing boards have more bigger buoyance force as more wider width and more bigger lift force as more faster velocity due to flow field. So in the case of beginner, he need to choose a board which has more wider width and in the case of expert, he will be choose a board which has more narrow width and is more lighter becase the board can have more faster velocity. When a person ride into surfing board then if he sustain the balance between the right and left, then the surfing board will be in the swim by buoyancy force. So the beginner will need to concentrate to balance between right and left and he need to choose more wider board because the beginner swim more slowly than expert so his board is more influenced by buoyance force than lift force. In contrast with this case, expert boarder will swim easily with narrow surfing board only if his board has some high velocity, because the lift force due to flow field is large although the buoyance force is small.