WINDTUNNEL TESTING
Once an optimum shape is settled upon the sail now enters a purely analytical aspect of the sail design process, finite element analysis and pressure distributions. To get meaningful information from finite element analysis we must consider the properties of the material used to make the sail in addition to the loading on the sail. Since sailcloth is non-isotropic in it stretch resistance we utilize a polar plot of the materials resistance to stretch, and the placement or alignment of this material in the sail. Since sails are dynamic in their use and do not have one load path that handle all conditions and trim. The placement and aligment of the material utilized is an important aspect of the optimization process. Therefore the material selected must have ample strength in all directions to handle the dynamic loading. To help us understand these types of loads we generate stress and strain graphs of the sails. These graphs analyze the sail and allow adjustments to the design or shape of the sail, these adjustments are made to bring the sail into predetermined stress/ strain limits. The output from this process is a loaded 3-D sail shape taking into account initial 3-D shape, material properties and alignment, wind speed and direction. This deformed 3-D shape is then brought back into the design program.
* Stress: F/A, or the load divided by cross sectional area.
* Strain: (Li-Lo)/Lo, or Deformation in length divided by original length.
* Modulus "E" = Stress / Strain, is the slope of the straight line portion of the stress strain diagram.
