In this section we will look at some tools to display the curvature on curves and surfaces. We will go through a number of steps displaying the curvature on a curve and making simple modifications to the curve to improve the fairness.

Ø  In Maxsurf, go to the Profile view window

Ø  Open the BasicFairingSpline_Start.msd file

You will see something like this:

You can see that the left side of the curve only contains a few control points, while the right side has the control points much more densely spaced. A lot of the control points on the right can be removed without changing the shape of the curve while improving the fairness of the curve. But how do you actually judge the fairness of this curve? This is where you need some display tools like Curvature porcupines and compress.

 View a video that will show you the different curvature display tools for curves such as Curvature porcupines and Compress view. The video will also show some steps to manually improve the fairness of this curve. [Web | Disk]

Curvature Porcupines

The curvature on contours may be displayed in the form of porcupines.

Ø  Select the spline curve

Ø  Now select Show Curvature from the Display | Curvature menu or using the toolbar button below:

You will see something like this:

Ø  Read about curvature porcupines in the Maxsurf manual.

 Note: The value of the smallest radius (tightest bend) on a given curve is displayed numerically at the end of the porcupine located at the corresponding position on the curve.

You can also see that the curvature porcupines change sides from the upper to the lower side of the curve. This means that the curvature direction changes from positive to negative or visa versa. Changing of the curvature direction may be classified as an inflection. There are a number of inflections in this curve:

Inflection 1 may be classified as unfairness, whilst inflection 2 may be a feature of this curve.

Ø  Increase the longitudinal stiffness of the curve from 3 to 4 using the Surface Properties dialog from the Surfaces menu.

By increasing the stiffness the curvature discontinuity is reduced.

Ø  Remove one control point from the inflection area

Ø  Space the control points in the area so that they are evenly distributed by moving the middle control point as shown below.

Ø  Adjust the height of the middle control point to remove the inflection and produce a continuous curvature along the curve in this area.

You should now see something like this:

The surface fairness can be improved by increasing the surface stiffness, removing control points and spacing the control points evenly.

Ø  Now continue removing control points nr 4, 6, 8 and 9

This again leads to a dramatic improvement of the fairness. See BasicFairingSpline_EndCurvature.msd file.

You should use the stiffest spline and minimum number of control points that will give the desired shape.

Now let’s use the compress curvature display tool to further improve the fairness of this curve.

Compress

This expands the transverse and vertical axes in relation to the longitudinal axis in the plan and profile views. This can be helpful when fairing long, slender hulls.

Ø  In Maxsurf Profile window, open BasicFairingSpline_EndCurvature.msd

Ø  Select Compress from the Display menu

We can now see that the fairness can be further improved by distributing the amount of curvature along the length of the curve better so that we end up with something like this:

Exercise: Try fairing the curve by using the compressed view to produce a curvature distribution similar to the one above.

A few pointers:

Ø  Whatever you do, don’t touch the corner control points (1 and 9)!

Ø  Distribute the control points evenly long the curve, with a steadily reduced space between the control points on the right side of the curve

Ø  Move the control points up and down in small increments

Tip: you can use the arrow keys of your keyboard to move a control point up and down 1 mm at a time.

Continue with the Display the Curvature on a Surface section.