Design rule purpose
The purpose of this design rule is to ensure that options that Optioneer generates are feasible from installation point of view. For offshore applications, this is usually due to vessel manoeuvrability. Cable installation requires that a few fundamental conditions are adhered to:
there are minimum length, straight run-in sections at the beginning of the route (from the perspective of offshore substation) and at the landfall
that minimum radius of curvature is retained so that cable can rest on the seabed and the vessel can feasibly follow the required path
the route is kept straight wherever possible
As a result of this design rule, routes produced by Optioneer appear more intuitive to designers and require less refinement before a centerline can be converted into a route position list (RPL).
How to configure
The example below is simplified and a bit exaggerated to illustrate the point. It shows a pretty standard and simple offshore route which demonstrates various aspects of route geometry which can be enforced on Optioneer.
Optioneer performs curvature calculations on every point along the route and if the radius of curvature is too low, the route section is deemed infeasible and Optioneer will alter the route to attempt finding a feasible solution. We will continue with this route as an example, but Optioneer will always prioritise returning feasible routes to users - in other words, you are unlikely to get a route with issues like the one below!
N.B: Percentage of straight sections in the route isn't an objective as such. It is just a useful piece of data that Optioneer exports to users.
As Optioneer draws continuous curves (using cubic splines) rather than straight-curve segments, some sections of the route can benefit from manual 'straightening' and might often appear as curved sections with a very high radius of curvature. The value of radius of curvature that is large enough to consider a section straight is a parameter that can be configured (the default value is R=15,000m).
There isn't an explicit parameter that will make Optioneer approach the landfall point at a close-to-perpendicular angle. This means that putting a waypoint a few hundred meters before the actual landfall point, to indicate preferred 'direction of approach' is useful.
Waypoints might make routes infeasible if placed too closely together as the curvature constraint becomes impossible to satisfy.
Input / output summary
This design rule doesn't require a dedicated dataset and only performs geometry calculation on the route itself.
Min. horizontal turning radius of curvature
Radius of curvature to consider the route section to be approximately straight
Length of required straight section at the start of the route (offshore substation)
Length of required straight section at landfall
This design mainly ensures that the shape of the route is correct.
Value of horizontal radius of curvature at every point of the route
Plot on the vertical chart
Proportion of route that is approximately straight