In-depth
Figure 1 relational element radial slice. Figure 3 irregular waterline offsets through a propeller pocket.
Figure 2 Propeller required for CFD. Attributes of such
performance, calculations would include:
Kaplan 4.55 in 19a
•
Description of hull and propeller
nozzle. distributions using “elements”.
•
Predictions are well behaved with no
unusual results.
•
Any set of data can be applied.
No special knowledge of element
modelling is required.
•
Fast calculation times.
The relative simplicity of relational
element calculations also allow for
empirical connections that improve
accuracy of results. Two examples of
HydroComp’s opinion about CFD is table below. Statistical methods are empirically enhanced relational element
that it is downright amazing for what it convenient, cost-effective and accessible calculations are presented below.
does – but it does not do all things. to virtually any naval architect, but
The International Towing Tank the scope of their solution is limited, Example – Propeller design
Conference states it well: “Computational more-or-less, to parametric data. and analysis
capabilities are making inroads in the Highly complex codes like CFD, on A hybrid Propeller Design and Analysis
design and evaluation processes for the other hand, offer the ability to fully tool from HydroComp utilises a
many vehicles of interest including define the three-dimensional surface fundamental vortex lattice lifting-line
marine vehicles.” … “It is inevitable of the propeller or hull. Such codes, code for moderately loaded propellers,
that these methods will have an even however, are costly both in terms of with a connection to empirical data.
larger role in the future as computer computation time and resources. It is The lifting line code is the numerical
power increases and the application of not uncommon for computation time to underpinning of the tool, providing for
such codes further matures. However, exceed 20 minutes for a single generation, analysis of radial variations of shape,
it will still take considerable effort to with hundreds of generations required such as chord, thickness, camber, and
have the confidence in these methods for a complete analysis. [Brizzolara pitch. (This is illustrated in the graphic
that currently exists with the model 2009] below.) It also includes definition of
tests as grid resolution and turbulence “Relational elements” are a term axial and tangential wake velocities.
modelling drives the accuracy of the for the category of calculation that Most lifting-line codes use a generic
solution.” straddles the ground between the solely value for drag coefficient, whereby
parametric and fully three-dimensional. this new code allows empirical
hybrid empirical – These solutions allow for practical improvements as the user can select
computational solutions global variations that are not available from a list of foil types (such as NACA
Consider the three categories of in statistical methods, but without the 66 mod, Segmental, and Bi-Circular).
analytical solution offered in the complexity, cost, or specialised training The characteristics of the foil, such as its
The Naval Architect January 2010 33
NA Jan 10 - p32+33+
34.indd 33 12/01/2010 09:56:04
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80