Stabilised line of sight optical payloads for maritime vessels require variable platform conditions
during the development, test and evaluation phases. A ship deck motion simulator is one means of
generating such conditions in a controlled laboratory environment. This dissertation describes the
aspects of the modelling, identification and validation of a ship motion simulator, in the form of a
pneumatically actuated 3-DOF modified Gough-Stewart manipulator, to generate a realistic simulation
environment for controller design. The simulation environment is a Matlab? supervised MSC
ADAMS?/Matlab? Simulink? co-simulation in which Simulink? houses the pneumatic model, the
friction model, and the controller, and ADAMS? runs the dynamic model of the physical hardware.
A similar simulator cannot be found in published literature forcing a development of the model from
the ground up, using published information as a foundation. The simulator model is broken up at the
subsystem level which comprises the valve mass flow model, the piston chamber and force model,
the complete actuator model and finally the complete ship simulator model. Each of these is derived,
identified, and validated. The requirements of the simulator as well as the simulation environment
is derived from real-life measurements done on seafaring vessels. An inverse kinematic solution is
presented as a set of lookup tables which are generated from the outputs of MSC ADAMS? by manipulating
the simulator platform over the whole range of movements through Matlab?. The reverse
of the process is then used to ensure that actuator extensions generate the correct platform attitude -
the attitude errors as shown to be infinitely small. Two valve mass flow models are proposed, a classical
model and an ISO model, the first derived from thermodynamic principles and the second based
on the ISO-6358 standard. The parameters of the two models are identified through experimental
charging and discharging of a constant volume pressure chamber and sampling the temporal pressure
and temperature outputs. The mass flow is calculated from the measured data through parameter estimation.
Validation is done by comparing the temporal pressure outputs of the models with the actual
measured pressure signals. The mean absolute error for the best fit ISO model is less than half of the
Classic model at 0.4 MPa (MAE < 2 kPa) and the temporal pressure relationships in the closed-loop
and open-loop tests shows a 93% correlation against measured pressure signals. The combination
of the derived actuator chamber model and the valve mass flow model produces a realistic actuator
model. The force equation of each of the actuators makes provision for a nonlinear friction component.
The actuator friction model is based on a simple stick-slip relation with an acceleration dependent
Stribeck function and an exponential viscous friction component. This model is also identified with
data from the actual hardware. The complete ship motion simulator model is validated through openloop
as well as closed-loop tests. The open-loop tests are performed with chirp or sinusoidal signal
excitation from a stable elevated offset starting condition. The ratio of the measured and simulated
extension amplitudes in the open-loop is larger than 0:95 while the ratio of the rise times (tm=ts) is approximately
0.85. The closed-loop validation tests are conducted with both heave and roll inputs and
compared well with the real system. A 14% difference in the actuator position amplitude (between
the simulated and measured systems), and a 20% slower extension rate at 0.05 Hz that increases at
1 Hz to match the measured rate are observed. The maximum large signal bandwidth is 0:617 Hz,
and is only limited by the mass flow. A simplified plant model is derived and compared with the high
performance model and is subsequently used for a state feedback controller design and evaluation.
The final controller gains deliver a stable system with the same 0:617Hz bandwidth limitation and a
controller that is insensitive to loop gain changes from 0.5 to 15.
Optiese loonvragte vir maritieme vaartuie, waarvan die siglyn gestabiliseer word, benodig veranderlike
platform toestande tydens ontwikkeling, toets en evaluasie. Een manier om veranderlike dektoestande
in ?n laboratorium te emuleer, is deur ?n skeepsdeksimulator te gebruik. Hierdie verhandeling
beskryf aspekte van die modelering, stelsel identifikasie en validasie van ?n drie grade van vryheid
skeepsdeksimulator wat gebruik word om ?n realistiese simulasieomgewing te skep. Die simulator
is in die vorm van ?n gemodifiseerde pneumatiese Gough-Stewart manipulator. ?n Gesamentlike
MSC ADAMS?/Matlab? Simulink? simulasie, wat deur Matlab? bedryf word, vorm ?n simulasieomgewing
waarin ADAMS? die dinamiese model van die fisiese hardeware huisves, en Simulink?
die pneumatiese model, die wrywingsmodel en die beheerder hanteer. Daar kan geen soortgelyke
simulator gevind word in gepubliseerde literatuur nie, wat tot gevolg het dat ?n model van eerste
beginsels opgestel is deur die gepubliseerde inligting as fondasie te gebruik. Die simulasiemodel is
opgebreek op substelselvlak wat die massavloei model van die klep, die silinderkamermodel, sowel as
die kragmodel van die suier, die volledige aktuatormodel en ook, laastens, die volledige skeepsdeksimulatormodel
insluit. Al hierdie modelle is afgelei, die parameters ge?dentifiseer and gevalideer.
Die behoeftestellings van die simulator, sowel as die simulasieomgewing, is afgelei uit werklike metings
van soortgelyke seevarende vaartuie. Opsoektabelle, wat bereken is deur met Matlab? die simulatorplatform
binne MSC ADAMS? deur sy volledige bewegingsberyk te manipuleer, stel die inverse
kinematika voor. Infinietdesimale klein foute is verkry deur die proses in tru aan te wend en die
platform ori?ntasie tydens verskeie aktuatortposisies te toets. Daar is twee klep massavloeimodelle
beskryf, ?n klassieke model wat van basiese termodinamiese geginsels afgelei is, en ?n ISO model
wat gebaseer is op die ISO-6358 standaard. Beide hierdie modelle se parameters is deur eksperimentele
stelselidentifikasieprosedures bepaal tydens opblaas- en afblaastoetse. Hiervoor is ?n konstante
volume druktenk gebruik en beide die tydafhanklike interne druk en lugtemperature is gemeet.
Die massavloei is bepaal deur parameterestimasietegnieke toe te pas op die voorgestelde modelle, en
validering deur die tydafhanklike druk te vergelyk met die uitsette van die modelle. By ?n werksdruk
van 0.4 MPa is die gemiddelde absolute fout van die ISO model minder as die helfte van die fout van
die klassieke model (MAE < 2 kPa), en die tydafhanklike drukverwantskap in beide die geslotelus-,
sowel as die ooplustoetse toon ?n 93% korrelasie teen die gemete drukwaardes. Die kombinasie van
die afgeleide silindermodel en die klep massavloeimodel lewer ?n geloofwaardige wrywingslose aktuatormodel,
en deur die dinamiese kragvergelyking te gebruik, word dit aangevul deur ?n nie-linie?re
wrywingskomponent. ?n Steek-glip wrywingsmodel met ?n versnellingsafhanklike Stribeckfunksie
en ?n eksponeti?le viskeuse wrywingskomponent stel die aktuatorwrywing voor. Die wrywingsmodel
is ook ge?dentifiseer deur werklike gemete data. Die valideringsoefening van die volledige skeepsdeksimulator
is voltooi deur beide ooplustoetse, sowel as gelotelustoetse uit te voer. Die ooplustoetse is
vanaf halfuitgestrekte aktuatorposisies gedoen deur sinuso?dale en tjirp opwekkingsseine te gebruik.
Die amplitudeverhouding tussen die gemete posisies en die gesimuleerde posisies is groter as 95%,
terwyl die stygtydverhouding (tm=ts) ongeveer 0.85 is. Vir geslotelusvaliderinstoetse is beide deining
and rol stelpunte as insette gebruik en die simulasie resultate is met die werklike gemete waardes
vergeleik. Die gemete amplitude van die aktuatorposisie is ongeveer 14% kleiner as die gesimuleerde
amplitude, die gemete aktuatorspoed is ongeveer 20% stadiger by 0.06 Hz en terwyl dit ongeveer
dieselfde is by 1 Hz. Die maksimum grootseinbandwydte is 0.617 Hz en word beperk deur die massvloeivermo?
van die klep. ?n Vereenvoudigde stelselmodel is afgelei, ?n toestandsterugvoerbeheerder
is ontwerp en die beheerder ge-evalueer met beide die ho? akkuraatheid model, sowel as die vereenvoudigde
model. Die finale beheerder lewer ?n stabiele stelsel met dieselfde 0.617Hz bandwydte wat
onsensitief is vir luswinsveranderinge vanaf 0.5 tot 15.
