Practical Ship Hydrodynamics

Introduction 19
ship. Inner flow computations may be coupled to the outer (global) motions
of a ship. Related problems are flows in a roll damping tank, sloshing, and
water flowing into a damaged ship.
Table 1.1 summarizes an assessment of the maturity of the various CFD applications.
Table 1.1 Maturity of CFD application on
a scale from – (not applicable, no applications
known) to žžžž (very mature)
Viscous Inviscid
‘Resistance test’ žž žžž
‘Propulsion test’ žž –
Manoeuvring ž ž
Ship seakeeping ž žž
Offshore – žžž
Propeller ž žžžž
Others ž –
1.4.4 Cost and value aspects of CFD
The value of any product (or service) can be classified according to time, cost
and quality aspects. For CFD this means:
ž Time benefits (How does CFD accelerate processes in ship design?)
In the shipbuilding industry, we see the same trends towards ever decreasing
times for product development as in other manufacturing industries. In some
cases, delivery time is the key factor for getting the contract. CFD plays
a special role in this context. A numerical pre-optimization can save timeconsuming
iterations in model tests and may thus reduce total development
time. The speed of CFD allows applications already in preliminary design.
Early use thus reduces development risks for new ships. This is especially
important when exploring niche markets for unconventional ships where
design cannot be based on experience. In addition, another aspect related to
turnover has to be realized: CFD improves chances of successful negotiations
by supplying hydrodynamic analyses. It has become almost standard
for all high-tech shipbuilders to apply at least inviscid CFD analyses to
proposed hull designs when entering negotiations to obtain a contract for
building a ship.
ž Quality benefits (How does CFD enable superior ships or reduce risks in
new designs?)
Model tests are still far more accurate for power prognosis than CFD. We see
occasionally good agreement of CFD power prediction with measured data,
but these cases may just benefit from fortunate error cancellation or tuning
of parameters to fit a posteriori the experimental data. No ‘blind’ benchmark
test has yet demonstrated the ability of CFD codes to predict, at least with
5% accuracy, consistently the power of ship hulls at design speed. I expect
this to remain so for some more years. Long-term CFD should outperform
model tests, as with growing computational power, accurate simulations at