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A Low-Level USV Controller Incorporating an Environmental Disturbance ObserverUnknown Date (has links)
Modeling, system identification and controller design for a 16’ catamaran is
described with the objective of enhanced operation in the presence of environmental
disturbances including wind, waves and current. The vehicle is fully-actuated in surge,
sway and yaw degrees of freedom. Analytical and experimental system identification is
carried out to create a numerical model of the vehicle. A composite system of a Multiinput
multi-output Proportional-Derivative (PD) controller and a nonlinear disturbance
observer is used for station-keeping and transiting modes of operation. A waypoint
transiting algorithm is developed to output heading and cross-track error from vehicle
position and waypoints. A control allocation method is designed to lower azimuthing
frequency and incorporate angle saturation and rate limits. Validation is achieved with
improvement in simulation with the addition of the nonlinear observer. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection
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The design of a hydrofoil system for sailing catamaransLoveday, Howard 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / The main objective of this thesis was to design a hydrofoil system without a trim and ride height control system
and investigate the change in resistance of a representative hull across a typical speed range as a result of the
addition of the hydrofoil system, while retaining adequate stability.
The secondary objectives were as follows: Find a representative hull of sailing catamarans produced in South
Africa, and to establish an appropriate speed range for that hull across which it is to be tested. Test and explain
the drag characteristics of this hull. Find a suitable configuration of lifting foils for this hull that would not
require any form of trim or ride height control to maintain stability throughout the speed range. Test and
compare the resistance characteristics with and without the assistance of lifting foils. Test and explain the effects
of leeway and heel on the total hydrodynamic resistance both with and without lifting foils.
A representative hull (RH1), based on a statistical analysis of sailing catamarans produced in South Africa and
an existing hull design of suitable size, was designed. A speed range was then established (0 – 25 knots) based
on the statistics of the original (existing) design. A scaled model (of RH1) of practical and suitable dimensions
was designed and manufactured, and its characteristics determined through towing tank testing.
A hydrofoil system was then designed and during testing, was adjusted until a stable configuration was found.
This resulted in a canard type configuration, with the front foil at the bow and the main foil between the
daggerboards. Although a stable configuration was achieved, it was noted that any significant perturbation in
the trim of the boat would result in instability and some form of trim control is recommended.
The main objective was achieved. The experimental results concluded that a canard configuration was found to
be stable for the RH1 (foil positioning already mentioned) and the addition of the hydrofoils provided a
significant improvement only above a displacement Froude number of 2, which for our full scale prototype, is
equivalent to approximately 14.2 knots.
This is in agreement with the results of several other research projects that investigated hydrofoil supported
catamarans with semi‐displacement type demi‐hulls. Below displacement Froude number of 2, a significant
increase in total hydrodynamic resistance was observed. Since the speed of sailing craft is dependent on wind speed, there will often be conditions of relatively low boat
speed (below displacement Froude number of 2). So it was recommended that a prototype design would have a
retractable hydrofoil system which could be engaged in suitable conditions (sufficient boat speed).
The effects of leeway and heel on the total hydrodynamic resistance were determined experimentally, but it was
found that these trends were affected by the resulting changes in wave interference resistance. Since wave
interference depended strongly on the hull shape, it was therefore concluded that no universal trends can be
determined regarding the effects of heel and leeway on the total hydrodynamic resistance. These effects were
determined for RH1 and it was shown that these effects are drastically altered by the addition of the lifting foils.
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A passive suspension system for a hydrofoil supported catamaranKopke, Markus 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / This study investigates practical passive methods to improve the seakeeping of a
Hydrofoil Supported Catamaran (Hysucat). The Hysucat is a hybrid vessel combining
hydrofoil efficiency with the stability of catamarans.
The seakeeping of the Hysucat was initially investigated experimentally to determine
what seakeeping improvements are inherent to the Hysucat design. The results
showed that the seakeeping is improved by 5-30%.
A passive suspension system for the main hydrofoil of the Hysucat was designed and
tested. A concept development strategy was followed for the design of the suspension
system as such a system had never been investigated previously. Detailed
specifications for the design were developed and concepts that could satisfy the
customer and engineering requirements were generated.
Numerical simulation models for the Hysucat and the final concepts were derived
assuming a simplified 2nd order system to describe the seakeeping dynamics of the
demi-hulls. Unknown parameters were determined using parameter estimation
techniques. Representative parameter values were calculated from multiple towing
tank experiments. Theory describing the motion of a hydrofoil in an orbital velocity
wave field was combined with the hull model to simulate the Hysucat as well as the
suspension system concepts.
The models indicated that the concept where the main hydrofoil was attached to a
spring loaded arm, that was free to pivot in response to orbital waves, was the most
feasible in damping out vertical transmitted accelerations. Experimental tests indicated
that little improvement was achieved with the suspension system at low frequencies. At
resonance the suspension system was effective in decreasing the heave of the vessel
by up to 27%. The pitch and acceleration response results showed improvements at
the higher encounter frequencies of up to 50%. The calm water resistance of the vessel
increased by 10% over the Hysucat with rigidly attached hydrofoils; however was still
24% less than the hull without foils.
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Design and optimization of hydrofoil-assisted catamaransMigeotte, Gunther 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: This work is concerned with the hydrodynamic design of hydrofoil-assisted catamarans.
Focus is placed on the development of new and suitable design methods and
application of these to identify the most important geometric parameters of catamaran
hulls and hydrofoil configurations that influence efficiency and performance. These
goals are pursued by firstly gaining a thorough understanding of the governing hydrodynamic
principles involved in the design process. This knowledge is then applied to
develop new and improved experimental techniques and theoretical methods needed
for design. Both are improved to the extent where they can be applied as design
tools covering the important semi-displacement and semi-planing speeds, which are
the focus of this study.
The operational speed range of hydrofoil-assisted catamarans is shown to consist of
three distinct hydrodynamic phases (displacement, transition and planing) and that
different hydrodynamic principles govern vessel performance in each phase. The hydrodynamics
are found to differ substantially from that of conventional high-speed
craft, primarily due to the interaction between the hull and the hydrofoils, which
is found to vary with speed and results in the need for more complex experimental
procedures to be followed if accurate predictions of resistance are to be made.
Experimental predictions based on scaled model tests of relatively small hydrofoilassisted
catamaran models are found to be less accurate than that achievable for
conventional ships because of the inability to correct for all scaling errors encountered
during model testing. With larger models scaling errors are encountered to a lesser
degree. The most important scale effect is found to be due to the lower Reynolds
number of the flow over the scaled foils. The lower Reynolds number results in higher
drag and lower lift coefficients for hydrofoils compared with those achieved at full
scale. This effect can only be partially corrected for in the scaling procedure using
the available theoretical scaling methods.
Presently available theoretical methods commonly used for the design of conventional
ships were found to be ill adapted for modeling the complex hydrodynamics
of hydrofoil-assisted catamarans and required further development. Vortex lattice
theory was chosen to model the flow around hydrofoil-assisted catamarans as vortex
theory models the flow around lifting surfaces in the most natural way. The commercial
code AUTOWING is further developed and generalized to be able to model the
complex hull-hydrofoil interactions that change with speed. The method is shown to
make good predictions of all hydrodynamic quantities with accuracies at least as good
as that achievable through model testing and therefore fulfills the requirements for a
suitable theoretical design tool.
The developed theoretical and experimental design tools are used to investigate the
design of hydrofoils for hydrofoil-assisted catamarans. It is found that the main parameter
needing consideration in the hydrofoil design is selection of a suitable hydrofoil
lift fraction. A foil lift fraction in the order of 20-30% of the displacement weight
is needed if resistance improvements using hydrofoil assistance are to be obtained
over the hull without foils. It is often more favorable to use higher foil lift fractions
(50%+) as the resistance improvements are better, although careful attention should
then be given to directional and pitch-heave instabilities. The Hysuwac hydrofoil
system patented by the University of Stellenbosch is found to be hydrodynamically
optimal for most hullforms.
The hullform and in particular the curvature of the aft buttock lines of the hull are
found to have an important influence on the achievable resistance improvements and
behaviour of the hydrofoil-assisted hull at speed. Hull curvature is detrimental to
hydrodynamic performance as the suction pressures resulting from the flow over the
curved hull counter the hydrofoil lift. The hullform best suited to hydrofoil assistance
is found to be one with relatively straight lines and hard chine deep- V sections.
The main conclusion drawn from this study is that hydrofoil-assistance is indeed
suitable for improving the performance and efficiency of catamarans. The design and
optimization of such vessels nevertheless requires careful consideration of the various
resistance components and hull-foil interactions and in particular, how these change
with speed. The evaluation of resistance for design purposes requires some discipline
between theoretical analysis and experimental measurements as the complexity of
the hydrodynamics reduce the accuracies of both. Consideration of these factors
allows hulls and hydrofoils to be designed that are efficient and also free of dynamic
instabilities. / AFRIKAANSE OPSOMMING: Hierdie studie is gerig op die hidrodinamiese ontwerp van hidrovleuel-gesteunde katamarans.
Daar word gefokus op die ontwikkeling van nuwe en geskikte ontwerpmetodes,
asook die toepassing van hierdie metodes om die belangrikste geometriese parameters
van katamaranrompe en hidrovleuel-konfigurasies wat 'n invloed op doeltreffendheid
en werkverrigting het, te identifiseer. As aanloop tot die studie is 'n deeglike begrip
van die onderliggende hidrodinamiese beginsels bekom. Hierdie kennis is toegepas om
nuwe en verbeterde eksperimentele en teoretiese tegnieke te ontwikkel wat nodig is vir
die ontwerp van hidrovleuel-gesteunde katamarans in die belangrike deels-verplasing
en deels-planering spoedbereike.
Daar word getoon dat die bedryfspoedbereik van 'n hidrovleuel-gesteunde katamaran
uit drie onderskeibare hidrodinamiese fases bestaan, naamlik verplasing, oorgang en
planering, en dat verskillende hidrodinamiese beginsels die vaartuig se werkverrigting
in elke fase bepaal. Daar is ook gevind dat die hidrodinamika wesentlik verskil van dié
van konvensionele hoëspoed-vaartuie, hoofsaaklik as gevolg van die interaksie tussen
die romp en die hidrovleuels wat wissel na gelang van die spoed. Hierdie interaksies
moet in ag geneem word gedurende die ontwerpproses en beide eksperimentele en
teoretiese metodes is nuttig om die omvang daarvan te bepaal.
Daar is gevind dat die eksperimentele voorspellings gebaseer op toetse met relatief
klein skaalmodelle van hidrovleuelgesteunde katamarans minder akkuraat is as dié wat
bereik kan word met konvensionele skepe. Dit is omdat al die skaalfoute wat tydens
die toetsing met die model ontstaan, nie gekorrigeer kan word nie. Die belangrikste
skaaleffek is as gevolg van die laer Reynoldsgetal van die vloei oor die afgeskaalde
vleuels. Groter modele Die laer Reynoldsgetal lei tot hoër sleur- en hefkoëffisiënte in
vergelyking met dié vir die volskaal-hidrovleuels. Wanneer die beskikbare teoretiese
metodes gebruik word, kan daar slegs gedeeltelik vir hierdie effek in die skaalprosedure
gekorrigeer word. Daar is ook vasgestel dat die skaaleffekte op die Reynoldsgetal
verminder word wanneer die hidrovleuels baie nabyaan die vrye oppervlakte is. Dit
lei daartoe dat eksperimentele voorspellings van werkverrigting meer akkuraat is vir
die ontwerpe waar die hidrovleuels nie so diep onder die water is nie.
Daar is gevind dat die teoretiese metodes wat tans beskikbaar is en algemeen vir
die ontwerp van konvensionele skepe gebruik word nie die komplekse hidrodinamika
van hidrovleuel-gesteunde katamarans kan modelleer nie. Die werwelroosterteorie is
gekies om die vloei om hidrovleuel-gesteunde katamarans te modelleer aangesien dié
teorie die vloei om hefvlakke op die natuurlikste manier weergee. Die kommersiële
kode AUTOWING is verder ontwikkel en veralgemeen om ook die komplekse spoed-afhanklike interaksies van die romp en hidrovleuel te kan modelleer. Hierdie metode
lewer goeie voorspellings van al die hidrodinamiese maatstawwe met akkuraathede
wat ten minste so goed is soos di wat met modeltoetsing bereik word en voldoen
daarom aan die vereistes vir 'n geskikte teoretiese ontwerpmetode.
Die teoretiese en eksperimentele ontwerpmetode wat ontwikkel is, word gebruik om
die ontwerp van hidrovleuels vir hidrovleuel-gesteunde katamarans te ondersoek. Daar
is gevind dat die belangrikste parameter wat in die hidrovleuel-ontwerp in ag geneem
moet word, die keuse van 'n geskikte hidrovleuelhefverhouding is. Om in rompe met
hidrovleuelsteun verbeterings in die weerstand te kry in vergelyking met rompe sonder
vleuels, is 'n vleuel-hef-verhouding van 20-30 persent van die verplasingsgewig
nodig. Dit is dikwels beter om hoër vleuel-hef-verhoudings (van 50 persent of meer)
te gebruik omdat die verbetering in weerstand dan groter is. Daar moet dan egter
gewaak word teen rigtings- en hei-hef-onstabiliteite. Daar is gevind dat die Hysuwachidrovleuel-
stelsel wat deur die Universiteit van Stellenbosch gepatenteer is, hidrodinamies
optimaal is vir die meeste rompvorms.
Daar is gevind dat die vorm van die romp en veral die kromming van die lyne gevorm
deur vertikale snitte deur die romp (Engels: "aft buttock lines") van die romp 'n
belangrike invloed het op die bereikbare weerstandsverbeterings en die gedrag van die
hidrovleuel-gesteunde romp wat op spoed is. Die kromming van die romp is nadelig
vir die hidrodinamiese werksverrigting aangesien die suigdruk as gevolg van die vloei
oor die gekromde romp die hefkrag van die hidrovleuels teenwerk. Die rompvorm wat
die geskikste is vir hidrovleuel-ondersteuning is 'n romp met relatiewe reguit lyne en
skerp hoekige diep- V seksies.
Die belangrikste gevolgtrekking waartoe tydens die studie gekom is, is dat hidrovleuelondersteuning
wel geskik is vir die verbetering van die werkverrigting en die doeltreffendheid
van katamarans. Die ontwerp en optimering van sodanige vaartuie verg
nogtans die noukeurige oorweging van die verskeie weerstandskomponente en rompvleuel-
interaksies en veral hoe hierdie interaksies verander met spoed. Die evaluering
van die weerstand vir die doeleindes van ontwerp verg dissipline tussen die teoretiese
analise en die eksperimentele metings aangesien die kompleksiteit van die hidrodinamika
die akkuraatheid van die algemeen-gebruikte teoretiese en eksperimentele
metodes vir die hidrodinamiese ontwerp verminder. As hierdie faktore in ag geneem
word, kan rompe en hidrovleuels ontwerp word wat doeltreffend is en ook vry is van
dinamiese onstabiliteite.
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Seakeeping control of HYSUCATsMilandri, Giovanni Sergio 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates practical methods of modelling and control of the vertical
motions of a hydrofoil assisted catamaran, the HYSUCAT. The aim of the
control application is to reduce the motions, and consequently the motion
sickness of the passengers.
First, a potential flowcommercial program, POWERSEA,was used to model
the system. This uses 2-D strip methods to model the planing hull-form of
the vessel, and the Peter du Cane hydrofoil theory for modelling of the foils.
These simulations are compared to experimental towing tank results, with fair
agreement at lower speeds, but limited applicability at high speeds. Thus for
the control design the agreement was insufficient.
As an alternative, a simple coupled 2 degree-of-freedom spring - mass -
damper model is proposed, for which the equations of motion are derived.
This has 9 unknown parameters; three of these aremeasured directly, two are
modelled, and the remaining four were identified using an experimental parameter
estimation technique. Representative parameter values were calculated
frommultiple experiments for application in the control design.
The design of a control system was based on the above model. First, an
output-weighted Linear Quadratic Regulator (LQR) was designed to obtain
the full state feedback gains. A non-linear ’bang-bang’ control design was
then implemented to try and speed up the response of the system. These
control strategies, as well as no control, were applied in the towing tank in
regular waves, with good results at low and medium frequencies. At the design
point, 32% and 65% reductions in rms motions were achieved for pitch
and heave, respectively. At high frequencies, though, not much improvement
was achieved due to the bandwidth limitation of the control system. The LQR
results were better overall (reduced motions) across the frequency range than
the bang-bang controller, as well as having a lower added resistance in waves.
The control design of the output-weighted LQR was then revised to be
based on alternative outputs, as a possible improvement. However, a further
two controller designs did not yield any noticeable improvement and were
not developed further.
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