North Sails Design Suite Software Expands with Flow™ and Membrain™

Among the tools most commonly used by North Sails designers are the Membrain and Flow modules, which apply wind pressure to a sail’s surface and calculate the load forces created. Designers pressurize their sail shapes virtually to discover what their flying shape will be in the intended range. Flow and Membrain work in tandem with the sail shape moving back and forth between them. Designers first analyze the structure in Membrain and continue by applying pressure to see how the shape deforms when pressure is applied in Flow. They continue this feedback “loop” of testing and correcting until they are happy with both the sails’ structural integrity and flying shape.

Take a shallow dive into the technical and often intriguing world of Membrain and Flow with the screen captures below. Want to know more? Read even more about North Design Suite Software here, and begin to understand the many ways design horsepower keeps North Sails at the forefront of sailing technology.

This image illustrating “Tip Vortex” was captured in North Design Suite Flow. When wind passes over a sail, the flow is disturbed more at the foot and the head of the sail, where it gets sucked from the high pressure side to the low pressure side, initiating the “vortex” which expands downstream. Flow Panel Code was introduced in 1984 and is still in use for upwind sails today. While this early version of Flow is less accurate than OpenFoam RANS, it is much quicker. Designers can run this type of analysis instantly, whereas RANS takes hours.
At left: This image of a Dubois 58 sail model was captured in MemBrain and demonstrates “Major Strain” or the amount of stretch occuring under applied pressure. The green areas signify the most amount of stretch in the sail (.0857%), whereas the deepest blue signifies no stretch. The small white lines represent the direction of the strain. At right: This capture shows a slightly different view within MemBrain, of strain analyzed per 3Di tape, measured in the direction of the tape. In this view, designers look at which tapes could potentially be removed (those deep, deep blue), and which will need additional reinforcement (red). They do this by adjusting the density of the tapes in those areas.
This Membrain capture shows the effect of pressure calculated in Flow (left image) and OpenFoam RANS (right image). Specifically, it shows the pressure distribution between the different sails on the rig, which all work together as a double slotted foil. Green and blue indicate high areas of pressure.
This image from Flow shows the close interaction between the headsail, mizzen and mainsail on a classic boat. The tip vortices merge and roll-up together in the downstream, illustrating the amount of induced drag.
Captured in RANS, this image illustrates the partially separated flow over the gennaker. One concept North designers work with is attached vs detached flow – where attached flow indicates areas of lift, and detached flow indicates areas of primarily drag. In this image, red indicates the area of the sail with attached flow, followed by areas where the flow detaches from the sail, marked by the zone in yellow.
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