359
1 INTRODUCTION
The primary task of the multipurpose boat is to
conductrescueoperationsduringfloods.Theboathas
to be adapted to: operate on unrecognised flood
waters, transport people and animals, carry motor
vehicles(e.g.ambulances).Hence,itissupposedtobe
equipped with life‐saving equipment allowing
intensive care trea
tment. The design of the boat (in
particularhullgeometry)shouldallowlandingonthe
shore and safely returning to deep waters. It is
necessary that main dimensions obey the law about
transport objects on public roads. The problem‐free
transport is crucial. Propulsion must guarantee
operation velocity at least 20km
/h. The boat maybe
operatedbysuchentitiesofthepublicserviceas:fire
brigades, ambulance, border guards, WOPR
(VolunteerWaterRescueOrganization),waterpolice.
It is assumed that it can be also used as an inland
cruiser with a wide variety of standard equipment.
Followingmaindimensionswereconsidered:
Lengthoverall7to8m,
Maximalbreadth2,5m
,
Maximaldraught0,4m.
2 HULLGEOMETRY.PRELIMINARY
RESISTANCEANALYSIS
Several variants of the hull shape were designed.
Figure 1 shows one of the final concepts of
underwaterhullpart.
Forinitialvariant,itwascalculatedresistanceand
the shape of free surface for range velocities: 4‐22
km/h.Itwasobservedtha
tforvelocitieshigherthan
15km/hthereisariskoffloodingadeckbythebow
The Analysis of Motion D
y
namics and Resistance of
the Multipurpose Boat Operating in Shallow Water
J
.Kulczyk&T.Górnicz
WrocławUniversityofTechnology,Wrocław,Poland
ABSTRACT: Polish ma
rket of small boats has been developed very dynamically in recent years. Market
competitionforcestheshipyardstobuildnewmoreefficienthullformsandtocutthecostofproductionas
well.Thisiswhymoderncomputersimulationprogramsareusedmoreoftenbynavalarchitects.Another
trendistodesignmoreuniversalshipstha
tmaybeusedbylargernumberofdiversifiedcustomers.Thispaper
presents project proposal of multipurpose boat hull form. The boat was design to fulfil the requirements
imposedbypublicserviceslikewaterpolice,firebrigades,andborderguards.Itissupposedtobeoperatedon
unexploredfloodplainsandothertypeshallowwaters.Theanalysisofboa
t’smotionwasbasedoncomputer
simulations.Theresistancecurvewasevaluatedwithtwomethods:comparisonstudyofmodeltestresults
ofsimilarships andCFD methods.The resultsobtained from Ansys Fluent andFINE/Marine systems were
comparedinthi
spaper.Itwasshownthattakingintoconsiderationdynamictrimandsinkagehasasignificant
impactonfreesurfacecaptureandresistancevalues.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 8
Number 3
September 2014
DOI:10.12716/1001.08.03.05
360
wave. Figures 2 and 3 shows free surface shape for
velocities15and22km/h.
Obtainedresultsalloweddevelopingnewvariants
ofthehull.6thgenerationisfinalone.Itistakinginto
account all of the requirements for construction
technology, and the operational purposes (e.g. bow
ramp‐allowingsmall
vehicle to enter on the deck).
Figure4showsthetheoreticalhulllines.
Figure1.Proposedgeometryoftheunderwaterpartofhull
Figure 2. Free surface, Va= 15 km/h
Figure 3. Free surface, Va= 22 km/h
Figure4.Finalhulllines
Thebottom was slightly rounded (spinned). Bow
part was also risen. This allows obtaining higher
maximalvelocity,withoutriskofdeckflooding.The
basic hydrostatic calculations results for a range of
draughtsfrom0.3mto0.7mareshownintable.1and
on Figure 5. The table shows also all the
basic
geometricparametersofthehull.
Table1.
_______________________________________________
Draught m 0,30,35 0,40,50,7
Amidships
_______________________________________________
WettedArea m^2 17,476 18,966 20,447 22,582 26,595
Prismaticcoeff(Cp)0,663 0,666 0,667 0,709 0,76
Blockcoeff.(Cb) 0,645 0,65 0,653 0,695 0,745
KBm 0,172 0,201 0,23 0,286 0,394
BMtm 1,845 1,582 1,385 1,072 0,743
BMLm 16,784 16,05 15,503 12,528 8,801
GMtcorrected m 2,017 1,783 1,615
 1,358 1,137
GMLm 16,957 16,25 15,733 12,814 9,195
KMtm 2,017 1,783 1,615 1,358 1,137
KMLm 16,957 16,25 15,733 12,814 9,195
Length:Beamratio3,058 3,198 3,33 3,349 3,369
Beam:Draughtratio 7,92 6,806 5,968 4,794 3,448
Length:Vol^0.333ratio 4,859 4,748 4,663 4,261 3,745
_______________________________________________
There were determined a preliminary resistance
curves with the prognosis of required power.
Resistance curve was determined on the base of
modeltestresultsofsimilarships[1].Inaddition,the
resistance was also calculated with commercial CFD
software. Figure 6 presents the results of the
resistance analysis. The graph shows
½ of total
resistance. This method of presentation was selected
because the boat was designed as a twin propeller
construction. In further propulsion analysis the
“optimisticʺprognosiswasused.
361
Figure 5. Hydrostatic results
Figure6.Halfshipresistance‐analyticalmodels
CFDcalculations
A final resistance curve was determined using
CFDcalculation.Numericalsimulationswerecarried
out with two commercial CFD codes: Ansys Fluent
andFine/Marine.
2.1 AnsysFluent
Initially, simulations were calculated in the Ansys
Fluent[2].Thissoftwarewasrepeatedlytestedandit
wasproven that isexcellent for the computations
in
thefieldofshiphydromechanics.Unfortunately,this
programdoesnot handlethe dynamicsimulation of
sinkage and trim of the boat. Due to the high
maximumvelocities(Fn=0.6)atwhichtheboatwas
tobeexploited,takingintoaccountthesephenomena
wasnecessary.
Thestructuralgridwas
used.Sizeofthegridwas
about 1 million of elements for half of the ship.
Duringtheconstructionofthecomputationaldomain
the symmetry condition was used. Wall function
modelused to determineflow close to no slipwalls
(dimensionlesssizeofthefirstelementofy+=40).
To
improve the stability calculations the ship was
accelerated from the zero velocity to first and next
measurement points, so unsteady calculation
approachwasused.Freesurfacewascapturedwith
ʺVolumeofFluidʺmethod.
2.2 FINE/Marine
Dynamic trim and sinkage was computed with
FINE/Marine software[2], this is a fully dedicated
computational system for simulating ship
hydrodynamics. In simulations there were used
unstructured grids, with hexagonal type elements.
Domains and their discretisation were made in
Hexpressprogram.Theinitialgridsizewasofabout
1.5millionsofelements.Forsomecalculationsitwas
useddynamicadaptivegridrefinementmethod.Final
size
ofthemeshwasincreased3times.
2.3 Results
Figure 7 presents a comparison of the resistance
curvesobtainedwithAnsysFluent,Fine/Marineand
the method of based on model test result of similar
ships.ForlowFroudenumbers,theseresultsarevery
similar.Withtheincreaseofthespeeddifferences
are
clearly noticeable. Resistance curve from
FINE/Marine is bend beyond Va=4.5m/s. This is
caused by increasing role of dynamic lift. Maximal
waveresistanceisexpectedforFroudenumber0.5in
thatcaseVa=4.5m/s.
Figure 7. Half ship resistance - numerical simulations
Figure 8. Comparison of wave system solved with Fluent
andFINE/Marine,Va=15kmh.
362
Figure9.Wavesystem‐sideview.Va=15kmh.
Figure10.Comparisonofbowwave.Va=15km/h
Figures7to9showthedifferencesinthecapture
of free surface generated by the two computing
systems. Bow wave (Figures 8 and 9) captured by
FLUENT seems to be unnaturally smoothed. The
significantdifferencesinthewavesystem(noticeable
especially in Figure 7) are the consequence of
differentfinal
dynamicdraughtandtrimangleofthe
ship.
Figure11.Dynamicsinkageinfunctionofvelocity
Figure12.Dynamictriminfunctionofvelocity
Figure 11 shows relation between draught of the
shipandboatvelocity.Abovethevelocity4.5m/sit
begins to play a dominant role hydrodynamic lift
acting on the flat bottom of the hull. Primarily boat
will be exploited in low velocities (Froude number
much less than 0.5). In case of
higher operational
velocities,flatbottomandsharplytruncatedsternwill
help to better utilize hydrodynamic lift force and to
improvethemotionbehaviour.
Figure12illustratesthetrimangleasafunctionof
velocity.Boathasatendencytotrimtothestern.This
isverybeneficialbecauseofthe
widebowpart.For
designreasonsthewidthofthebowwasimposedas
an external condition. There will be installed bow
ramp.
Figure13.Pressureandvelocitydistributiononthehull.
Figure 13 shows the pressure distribution on the
hull and velocity field close to boat surface. These
distributionsareuniform.Therearenosignsoflocal
peaks.Streamlinesareparalleltothesymmetryplane,
no recirculation zones were observed. Picture 14
shows dimensionless velocity distribution in
propeller ring zone. Wake field
in propeller area is
very favourable. There is only small wake peak
presentin12oʹclock.
Figure14.Wakefieldinpropellerring,Va=15km/h
Figure15.Boundarylayeralongthehull,Va=15km/h
Distribution of dimensionless velocities close to
thehullispresentedonFigure15.Boundarylayeris
formed evenly along the hull. There are no rapid
increases or decreases of boundary layer thickness.
363
No flow separation is expected close to the hull
surface.
3 SELECTIONOFPROPULSIONSYSTEM.
Initial determination of the parameters of the drive
systemwasbasedonfollowingassumptions:
Infurtheranalysistheoptimisticforecastisused,
Twin‐enginedriveisused,
Standardscrew‐typeB‐Wageningen
isused,
Powerofoneengineisanalyzedforrangefrom50
to125kW,
Theefficiencyofthetransmission‐eta=0.94,
Thepropellerdiameterisanalyzedforrangefrom
0.3mto0.6m
Impactfactorst=0.1;w=0.1.
Selection of propulsion drive system was
done
withhome‐developedprogram.Itisintendtodesign
screwpropellersonthebaseoftheperformanceofthe
series of propellers. For designed boat draught, the
boatcouldbeequippedwithtwoB‐Wageningentype
propellers, diameter D = 0.35 m, each driven by an
enginepowerPB=
50kW(2x50kWtotalpower).For
propellernominalrevolutionraten=33.3[1/s],itis
imposedtousegearwithratioi=1.5(enginenominal
revolution rate n = 50 1 / s). In table 2 there are
presentedresultsofcalculationsfortheotherdriving
motorsandpower
rangesaswell.
Table 2. The results of the preliminary calculation of
parametersofthedrivesystem
_______________________________________________
Nominalpower[kW] 125 100 75  50
Min.diameter[m]0,60,50,45 0,35
Gearratioi[‐]3 2 2 1,5
Efficiencyeta[‐]0,456 0,485 0,486 0,481
Velocity[m/s]5,628 6,135 5,914 6,057
Velocity[km/h]20,26 22,08 21,30 21,80
_______________________________________________
Taking into account the above results, it can be
assumed that two engines with a power of 50 kW
eacharelikelytoprovideoperational velocityspeed
over 20 km/h. At a velocity of 6.057 m / s Froude
number is 0.684. This means that the boat at this
speed shall
be travelling on hydrodynamic lift
condition.
4 SUMMARY
Duringrealizationofthisproject underwaterpart of
thehullwasdesigned.Hullshapewasselectedtouse
the boat in water rescue services. The main
dimensionsofthehullmustprovideontheonehand
maximum displacement on the other hand
allows
easytransportonpublicroads.
Hydrodynamic properties of the boat were
analyzed using the methods of computational fluid
dynamics. Resistance curve was determined using
modeltestresultofsimilarunits.Powerofpropulsion
systemwasselectedtoachievehighvelocitiesanduse
hydrodynamic lift force, in the case when the
boat
wonʹtbefullyloaded.
ACKNOWLEDGEMENT
Theresearch presented in thispaper was financially
supported in the framework of R&D project
INNOTECH‐In Tech‐Nr INNOTECH‐K2/IN2/55/
182813/NCBR/12.
LITERATURE
[1]E. Chale, W. Grywotz, H. Sager, Weiterentwicklung
universellverwendbarerundenergiesparender
Rundspantschiffe mit stufenweiser Verlangerung des
Mittelschiffes.BerichtNr1058,Duisburg.
[2]ANSYSFLUENTUserʹsGuide.Release14.0,2011
[3]FINE™/Marine v3 Flow Integrated Environment for
MarineHydrodynamics.Documentationv3.1a,2013