Simulation Modelling Performance Dynamics of Ship
Gas Turbine at the Load of the Ship’s
Synchronous Generator
Josko Dvornik
1
and Eno Tireli
2
1
Faculty of Maritime Studies, University of Split,
Zrinsko frankopanska 38, 21000 Split, Croatia
2
Faculty of Maritime Studies, University of Rijeka,
Studentska 2, 51000 Rijeka, Croatia
Abstract. Simulation modelling, performed by System Dynamics Modelling
Approach-MIT and intensive use of digital computers, which implies the
extensive use of, nowadays inexpensive and powerful personal computers
(PCs), is one of the most convenient and most successful scientific methods of
analysis of performance dynamics of nonlinear and very complex natural
technical and organizational systems [1].
The purpose of this work is to demonstrate the successful application of system
dynamics simulation modelling at analyzing performance dynamics of a
complex system of ship’s propulsion system.
Ship turbine generator is a complex nonlinear system which needs to be
analysed systematically, i.e. as an entirety composed of a number of sub-
systems and elements which are through cause-consequence links (UVP)
connected by retroactive circles (KPD), both within the propulsion system and
with the corresponding environment.
Indirect procedures of analysis of performance dynamics of turbine generator
systems used so far, which procedures are based on the use of standard, usually
linear methods, as Laplace’s transformation, transfer functions and stability
criteria, do not meet the current needs for information about performance
dynamics of nonlinear turbine generator systems.
Since the ship turbine generator systems are complex and the efficient
application of scientific investigation methods called qualitative and
quantitative simulation methodology of System dynamics will be presented in
this work. It will enable the production and application of more and varied
kinds of simulation models of the observed situations, and enable the
continuous computer simulation using high speed and precise digital
computers, which will significantly contribute to the acquisition of new
information about nonlinear characteristic of performance dynamics of turbine
generator systems in the process of designing and education.
Successful realization of this work, or qualitative and quantitative scientific
determination of a complex phenomenon of performance dynamics of load of
the ship electric network, or ship turbine generator system, will give a
significant scientific contribution to the fundamental and applied technical
scientific fields, and to interdisciplinary sub-directions of maritime transport,
exploitation of ship drive systems, mariners education, automatics, theory of
management and regulation, expert systems, intelligent systems,
computerization and information systems.
Dvornik J. and Tireli E. (2006).
Simulation Modelling Performance Dynamics of Ship Gas Turbine at the Load of the Ship’s Synchronous Generator.
In Proceedings of the 4th International Workshop on Modelling, Simulation, Verification and Validation of Enterprise Information Systems, pages
157-162
DOI: 10.5220/0002471301570162
Copyright
c
SciTePress
The contribution may also be significant in the process of education of the
present and future university mechanic and electric engineers in the field of
simulation modelling of complex organisational, natural and technical systems.
1 Introduction
Dynamic investigation of nonlinear engine (especially electric engine) systems is a
relatively considerable problem in the area of investigating performance dynamics of
ship’s propulsion systems.
Ship gas turbine, i.e. the ship turbine synchronous generator (BTSG),
belongs, undoubtedly, to a set of linear complex technical systems, which consist of
two main subsystems: turbine system and ship synchronous generator.
In this work ship three-phase self-excited synchronous generator (BSG) has
been treated as particular sensitive consumer which is driven by ship gas turbine,
which means that they are the main source of alternating voltage of ship energy
consumers.
Ship turbine generator system will be presented as a set of nonlinear
differential equations, or continuous simulation model of upper level, the so called
equations of state, so it will simultaneously be a discrete simulation model, because it
strictly complies with the selected value of the main computation interaction step DT.
2 System Dynamics Simulating Modelling of Twin Shaft Gas
Turbine
2.1 System Dynamics Mathematical Model of Twin Shaft Gas Turbine
Mathematical model of dynamic performance of gas turbine is presented like this
[11]:
)(
1
tfkkT
bbGG
=+
μμϕϕ
ωω
(1)
where:
ω
ϕ
- relative change of angular speed,
ω - turbine angular speed,
G
μ
- relative change of fuel consumption,
G
t
- absolute fuel consumption
By developing the equation a final differential form in explicit form is reached:
Equations of shaft of turbo compressor with low pressure – consumer:
()
1122G
1a
1
k)t(fk
T
1
dt
d
ωωω
ω
ϕϕ+μ=
ϕ
(2)
158
Equations of shaft of turbo compressor with high pressure:
()
211G
2a
2
k
T
1
dt
d
ωωω
ω
ϕϕ+μ=
ϕ
(3)
2.2 System Dynamics Qualitative Model of Twin Shaft Gas Turbine
Qualitative simulation models, or mental and verbal, structural model and flow
diagram of ship gas turbine for the explicit differential equation (2) will be:
Mental and Verbal Model. When relative variation of fuel consumption
μ
G
and
product k
2
*
ϕ
ω
2
are increasing, relative angular speed variation is also increasing,
resulting in positive cause-consequence relation UPV (+).
When relative variation of possible external act of cargo and product k
1
*
ϕ
ω
1
are
increasing, relative angular speed variation is decreasing and observed UPV(-) is
negative.
Further, when time of shaft running T
a1
is
increasing, relative angular speed variation
is decreasing, resulting in negative sign UPV (-).
Structural Model and Flow Diagram. In accordance to the developed mental and
verbal model, structural model and flow diagram in DYNAMO symbols [2] of the
equation of the state (2) follow:
DFIOM1T
FIOM1T
TA1C
K1
MIG
FT
KOM2C*FIOM2
+
-
-
-
+
-
+
FBL (-)
Fig. 1. Structural diagram of turbo compressor with low pressure.
159
TA1C
K1
MIG
FT
PRODU
DFIOM1T
FIOM1
Fig. 2. Flow diagram of turbo compressor with low pressure.
In observed system there is one feed back loop (FBL):
FBL1(-): FIOM1=>(-) DFIOM1T=>(+)DFIOM1T=>(+)FIOM1; with self regulating
dynamic character (-), because the addition of negative sign is odd number.
3 System Dynamics Simulating Modelling of Ship Synchronous
Generator
In this short paper, it is impossible to give a complete model; complete model (30
equations) has been presented in IASTED, Pittsburgh, 1998, 372-375, (7).
4 Computing Simulating Model of the Gas-turbo Generator
Simulation Scenario. Run of the turbine is triple-stage, which means that in TIME=1
second the turbine was accelerated by bringing the fuel. At 10% of the nominal
number of revolution in TIME=5 seconds fuel consumption was increased to the 35%
of the nominal number of revolution, and in TIME=10 fuel supply was increased,
and in that way “uniform” heating of turbine i.e. nominal number of revolution is
obtained. In TIME=20 PID regulator is involved, and in TIME=30 exciting of the
generator started. In TIME=30 stochastic load occurs.
Graphics results of the simulation:
160
Fig. 3. Relative angular speed variation, relative angular speed variation of second shaft,
generator electromagnetic moment, relative variation of fuel consumption.
After turn of the turbine in idling PID regulator is involved. PID regulator acts on fuel
supply and with this act brings number of revolution of turbine on nominal value.
Fuel consumption increases with switching on the synchronous generator, while the
number of revolution of both shafts varies relatively little. In regime of stochastic
load (we simulate alternating switch on and off of electric consumer generating
random number) attempt to stabilise output voltage with self-excited according to the
phase compounding scheme was not effective enough. After replacing this part of
assembly with electrical PID regulator, which is visible from the diagram, those
output voltages vary in permissible limits, although variations of load are extremely
unfavourable.
5 Conclusion
The application of System Dynamics Simulation Modelling Approach of the complex
marine dynamic processes revealed the following facts:
l. System Dynamics Modelling Approach is a very suitable software education tool
for marine students and engineers.
2. System Dynamics Computer Simulation Models of marine systems or processes are
very effective and successfully implemented in simulation and training courses as part
of the marine education process.
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161
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