Modern Windships; Phase 2
2. Project Strategy
Background
Strategy for Phase 2
Definitions
Background
At regular intervals during the last 30 years attempts to exploit the
wind energy for reducing the fuel consumption of ships have been made, but because of low
oil prices and the increasingly higher efficiency of modern diesel engines none of these
attempts have proven economically profitable. The rising environmental consciousness in
the latest years combined with the success story of the modern windmills has once again
breathed new life into the ideas of developing a modern wind ship. With the findings from
phase 1 of the project at hand a strategy for designing the modern WindShip was developed.
Strategy for Phase 2
For the design work in phase 2, Pelmatic Knud E. Hansen chose the
following strategy:
1) Choice of rig design:
| The difference between a traditional sailing ship and windships. |
| Traditional sailing ships. |
| Former ideas for a windship rig. |
| The rig design of the windship - phase 1. |
1.1) Brainstorming:
| CFD calculations of rig alternatives. |
| Wind tunnel tests of one or two of the alternatives. |
| Final choice of rig. |
2) Wind tunnel tests of above-water hull with rig.
3) Choice of under-water hull and propulsion devices.
4) Static force measurements of the windships hull in
towing tank (PMM tests).
5) Velocity prediction based on the results from the
wind tunnel tests of the above-water hull and the
static force measurements of the under-water hull.
6) Route simulation based on the results from the
velocity prediction and statistical wind data for 3
years on 6 routes world-wide.
7) Detailed rig design:
| Decision on design loads based on wind statistics. |
| Structural design and choice of materials. |
| FEM (finite element method) strength calculation and optimisation of the rig. |
| Detailed design of rig manoeuvring components. |
| Price and weight calculation. |
8) Economical feasibility study based on the route simulation
results and the calculated rig price.
The strategy outlined above indicated the need to:
| Design a better rig system than the one obtained in phase 1, incorporating higher lift
and less sail area. |
| Investigate the hull lines and appendages to get good manoeuvrability and low
resistance. |
| Develop a Velocity Prediction Program (VPP) using the Planar Motion Mechanism tests
(PMM) and wind tunnel measurements in order to predict ship speed depending of installed
power, wind speed and wind direction. |
| Perform weather routing and calculate realistic data regarding fuel consumption on a
specified route. |
| Make a commercial comparison on each chosen route with a conventional ship. |
| Visualise of the WindShip rig using 3D CAD systems. |
This strategy has removed many uncertain factors from the project,
therefore the results in phase 2 are considered to be well founded, reliable and
realistic.
Definitions
In the text of this report the following phrases and symbols have been
used, see Figure 1 below:
Figure 1. Definitions used in the report.
The most often used English phrases can be found in Table 1 below.
The absolute wind |
= |
The direction of the wind in
relation to the sea surface. |
The apparent wind |
= |
The direction of the wind in
relation to the moving ship. |
Ships heading |
= |
The direction the ships
centre line points. |
The leeway |
= |
The ships direction through
the water. |
Drift angle |
= |
The angle between the ships
heading and the leeway. |
The cord |
= |
A straight line from the leading
edge of the sail or wing to the trailing edge. |
The angle of attack or angle of
incidence |
= |
The angle between the cord of a
sail or the centre line of a symmetrical steel mast and the apparent wind. |
Upwind |
= |
Sailing with the apparent wind from
a forward direction. |
Reaching |
= |
Sailing with the wind from the side
(about 90° to the ships centre
line). |
Running |
= |
Sailing with the apparent wind from
an afterward direction. |
Lift |
= |
The force generated by the sail or
wing perpendicular to the apparent wind. |
Drag |
= |
The force generated by the sail or
wing in the direction of the apparent wind. |
Stem |
= |
A fixed size mass (batch) loaded on
product carriers, often 25-, 35- or 40.000 tonnes. |
HFO |
= |
Heavy Fuel Oil, heavy, cheap oil
used at sea, high contents of pollutants. |
MDO |
= |
Marine Diesel Oil, lighter, more
expensive oil used when in port, "cleaner". |
Table 1. English phrases, definition
The ships courses in relation to the apparent wind have been denoted as
follows, see Figure 2:
Figure 2. Wind direction names.
The aerodynamic forces "lift" and "drag" have been
defined as follows, see Figure 3:
Figure 3. Lift, drag etc,. definition of terms.
The lift and drag forces vary directly with the density of the air, the
sail or wing area and the square of the winds speed. It is accordingly convenient to
express these forces in terms of non-dimensional coefficients that are functions primarily
of the attitude of the sail or wing.
The lift force "L" and the drag force "D" (in N)
are given by the following expressions:
|
L = ½ r V2 S CL |
Equation 1 |
|
D = ½ r V2 S CD |
Equation 2 |
Where:
r |
= |
density of the air (1.21 kg/m3 at 20°C and 1013 mbar) |
V |
= |
velocity of the air in m/s |
S |
= |
area of the sail or wing in m2 |
CL |
= |
lift coefficient |
CD |
= |
drag coefficient |
|