One of the problems frequently found in wind farm project and construction is that road bends with a reduced radius often needs an additional widening to allow the passage of the trucks with the WTGs components.

Normally the biggest problems come with the blades. I suggest using a commercial software such as AutoTURN to estimate the actual additional road widening needed, because the tables provided by wind turbine manufacturers are almost invariably inaccurate and often based on wrong hypothesis.

The point is that there are too many variables to simplify the problem and give a single "one size fits all" value:

• Angle between entry and exit tangent of the bend: the lesser the angle, the bigger the widening.
• Type of vehicle (number of wheels, center of turning circle, dimensions).
• Different possible trajectories chosen by the driver.
• Use of real wheels independent control.

Simulating software are great because they use real word data: the trucks are equipped with GPS equipment and the movements of the vehicle is registered and transformed in an algorithm that allow to replicate it in your AutoCAD project, with realistic results and cost effective solutions.

In the next image the trajectory of the different components of the truck in a bend with reduced radius are detailed. If the tractor unit follows a path in the center of the road, the rear wheels (orange lines in the drawings) will need an additional road widening both before the beginning of the bend and inside the bend.

It will also be necessary to clear an area appropriate for the transit of the blade tip (outside the bend, cyan line in the drawing) and for the truck body (inside the bend, green line in the drawing).

Figure 1: Standard wind farm internal road bend

It is also noteworthy that most of the trailers for WTGs components transportation allow orientating rear wheels independently from guiding front wheels.

For this reason, the road widening can be completely internal to the bend (using the steering control of the rear wheels) or external, sweeping the area outside the bend.

These solutions are normally more demanding in term of additional required area. They are used in situation where, due to existing constraints (buildings, structures, property boundaries, etc.) the standard widening cannot be used and a solution only inside or outside the bend must be found.

Here you have an example of a widening only in the interior side of the bend:

Figure 2: Wind farm internal road bend. Widening only in the interior.

This is a non standard solution, and as you can see it needs more space.

The third possibility is to use only the area outside the bend:

Figure 3: Wind farm internal road bend. Widening only in the exterior side.

This solution needs an enormous amount of space, and we use it only in exceptional situations.

AutoTURN special transport simulation: pros and cons

Working in Vestas at dozen of wind farms worldwide I’ve had the opportunity to use frequently AutoTURN to simulate bends and other complicated maneuvers (for instance in towns or near existing structures) with special transports (mainly wind blades and tower section trailers).

Although it is not cheap (the price was almost 1800 € plus VAT: a lot of money, considering that it’s an AutoCAD plug in) I am satisfied with the software.

The main advantage is that you can check very quickly if you’re going to have a problem somewhere, even if you don’t have a topography (sometimes we work with a blurry Google Earth picture). It is very easy to use and intuitive at the beginning, and it includes the rear wheels remote control used nowadays.

Main drawbacks: there are only a few special vehicles for wind components transport in the library, so you have to make your own. I’ve replicated several Nooteboom trailers, as we often works with them, using the “personalized vehicle” feature.

Moreover it is not possible to simulate reverse gear. This is a big, big problem as several times we use it in real word situations. Workaround: I’ve modified a normal trailer (not a wind blade tow), and I use it when I desperately need reverse gear.

Third problem, many times it would be useful to simulate problems in 3D, as sometimes the tow get stuck somewhere in a vertical transition. There is an upgraded version who allows you to works in 3 dimensions, but it doesn’t include the vehicles we use in the wind industry, so it’s not useful. The only solution is to build a 3D model of the terrain as I explain in another post and see what happen below the truck. Unfortunately it takes many hours.

Wind turbines components transport problems

Transport related problems occupy a relevant percentage of time in my department.

It’s no big surprise, considering that the models that we are selling (V90, V100 and V112) have blades up to 55 meters.

Usually we have 3 different kinds of problems:

• Vertical transition curves (for instance on top of hills)
• Weight

Depending on the curve radius and the angle between the back and forward tangents, a widening may be needed. Unfortunately, due to the number of variables it’s really difficult to find a closed formula or to define this extra widening on an easy-to-use table.

For this reason, we use a software developed especially to solve this problems (AutoTURN, developed by Transoft solutions).

It is not the only available software: for instance below you can see one of this simulations, courtesy of Nooteboom and developed with their "in house" software for a 90 degrees V112 bend:

For the vertical transition curves the problem is more complicated, as there are even more variables (extension of the shock absorbers, number of wheels, height of the load and so on). For this reason we normally made a 3D model to work with, but this is a really time consuming work.

Below, and example of a problem I had to solve in 2010; it is a new curve that we built on an existing road because the existing curve radius (on the left) was too small. Due to the strong height difference from the beginning and the end of the new bend the trailer was touching below, and I've had to modify it after the construction. I've asked for an as-built of the situation, prepared a 3D model and defined point by point the new geometry.

The weight of the loaded truck is the third problem we face. Normally the nacelle is the heavier components, and the biggest problem is on the bridge we have to cross when we have to reach the construction site. If the bridge is relatively new usually it is possible to find the project or to know the load it is supposed to carry – the big problem comes with old bridge (sometimes even in stone) we meet around the world: in this case the only solution is to study it with the help on an external engineering.