PhD-Theses completed in 2007
CFD Simulation Supplemented by Experimental Methods to
Investigate Pneumatic Flows
Institut für Fluidtechnik der TU Dresden
Technische Universität Dresden, Dresden, Germany
The
development and optimisation of pneumatic components is a complex
problem necessitating considerable experimental research even today.
Computational fluid dynamics (CFD) simulation could
dramatically reduce this research investment: CFD simulation not only
can make flow relationships understandable, but also identify
parameters that significantly influence design. However, the
application of CFD in pneumatics is complicated by several factors. Few
systematic research results exist to determine and validate the quality
of flow calculations. Furthermore, there is a shortage of proven
application methodologies guaranteeing high-quality results. This
applies particularly to the unsteady air flow resulting from switching
or controlling pneumatic valves. This description shows that, at
present, the combined use of experimental and numerical methods
provides the best opportunity to investigate pneumatic flows:
• reference measurements to calibrate and validate
CFD simulation (numerical calculation) under conditions as simple as
possible,
• numerical calculations for systematic analyses
with respect to the influence and sensitivity of specific design and
operating parameters.
Uncertainties occurring during the preparation and running of a
simulation, as well as during the analysis of complex results, could be
reduced. On the basis of subsequent operating experience and expertise,
the numerical portion in the industrial development process could be
increased, thus avoiding the need for extensive and costly experiments.
The latter concern reflects this dissertation’s overriding
goal, that of technically and economically optimizing the application
of CFD simulation in the industrial development of pneumatic
components. To this end, possible applications of CFD for turbulent air
flow in pneumatic components, especially in pneumatic valves, were
tested, the knowledge of characteristic flow conditions improved, and
the results validated. This applies particularly to unsteady CFD
simulation with moving grids, for which a scientific application
methodology is being developed and investigated. It allows for
effective and reliable performance of high-quality calculations for
fluidic design in pneumatic components for industrial development.
Besides the issues of validity and application limits of CFD simulation
in pneumatics, this application methodology also includes a systematic
procedure for problem-oriented modelling of specific flow processes.
This dissertation provides a practical basis to concentrate on
optimisation of pneumatic components right from the start. In addition,
the understanding gained as a result of simulation and experiment
further contributes to insights into the relationships between valve
geometry, operating variables, flow characteristics, and component
performance (e.g., flow rate). These insights in turn can significantly
contribute to an optimal utilisation of the potential of pneumatic
components, particularly pneumatic seated valves. This dissertation
further identifies new developmental directions for the improvement and
optimisation of the valves researched. CFD simulation can provide
verifiable projections about the quality of products in an early phase
of development, thus contributing to significant reductions in
developmental time as well as associated costs.
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Energy-Saving Drive Systems for the Working Hydraulics in
Mobile Machinery – Electrohydraulic Flow Matching
Institut für Fluidtechnik der TU Dresden
Technische Universität Dresden, Dresden, Germany
The thesis deals with systematic investigation of a new kind of
electrohydraulic systems for the working hydraulics in mobile
machinery, characterized as „Electrohydraulic Flow Matching
(EFM)“. In these systems an electronic control is being used
instead of the hydraulic-mechanical signal processing in conventional
LS-Systems. The aim of the new concept is to combine fair costs and
robustness of the conventional LS-Systems with high energy saving
potential, good controllability and high flexibility of
electrohydraulic systems. The main focus of the work lies in the
proving of the functionality and performance of the new systems and
their qualifying for practical use in mobile machinery.
A systematic classification of the new
solutions results in a broad variety of generalized electrohydralic
circuits for the working hydraulics. Each basic circuit can be extended
by additional functions in order to meet demands of a specific mobile
application. Some EFM-systems with the highest potential for practical
use have been chosen for detailed investigations. They apply a
conventional load-compensated valve control with primary pressure
compensators and a commercial electrohydraulically controlled pump. The
essential difference between these systems is the concept of the
electronic control, which includes an open-loop or a closed-loop
flow control of the pump, or a pressure compensator position control.
The EFM-system with open-loop flow
control is based on the integrated, proportional electrohydraulic pump
control and does not need any specific control algorithm. The
controller design for other EFM-systems focuses on easy-to-implement,
single-loop PID-control algorithms. The control plant of the
closed-loop flow control EFM-System comprises merely the pump. The pump
dynamics is rather independent of the working point, so a very robust
controller can be designed. On the other hand the EFM-System
with position control of a three-way pressure compensator (unloading
valve) or two-way (individual) pressure compensators does not
completely exclude the interference of the system control with the
hydraulic consumers, because the load pressure variations are being
indirectly put through via the controlled spool position. The energetic
and controller demands are contradictory due to low damping of the
pressure compensators in the desired control position, where energy
losses are low.
This problem can be efficiently solved
by using the method of command variable adding, where the operator
control signals to the valves serve for a direct control of the pump.
In this manner the pump reacts immediately on operator demands and the
system has a very good response behavior. The superimposed pressure
compensator position control eliminates the remaining control
deviations. The behavior of the machine, e.g.
“soft” or “aggressive”, can be
easily adjusted to specific working conditions through variation of the
share of the command variable adding in the control.
The principle of flow matching enables
an explicit reduction of energy losses in comparison to the
hydromechanical LS-System. The pressure margin of the LS-system is
constant, while the pressure losses in EFM-systems depend on the pump
flow. The most energy saving is realizable in the fine control mode.
The energy losses in EFM-systems can even be minimized by using
sophisticated control strategies.
The investigated EFM-systems feature
also a much better dynamic behavior than the hydromechanical LS-system.
The control is far less dependent of load pressure variations and
reacts principally only on changes in operator demands. This improves
damping and shortens settling time while preserving a very good
response behavior. Therefore the new concept can successfully cope with
exacting demands on system dynamics in mobile machinery. A further
improvement of the dynamic behavior is achievable by adjusting the
electric control of the valves and the pump. An extension of the
electronic control circuit is the only necessary system modification
for realizing this effect.
A further potential for improving the
EFM-concept lies in the optimization of hydraulic components. A special
attention should be given to pressure compensators, aiming at
minimizing the sensitivity of the position control to flow
fluctuations.
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Development of Active Tilt Control for a Three-Wheeled Vehicle
Centre for Power Transmission and Motion Control
University of Bath, Bath, UK
The CLEVER Project was a European Union funded research project to
design and develop a low emission alternative vehicle for city
environments, which aimed to combine the comfort and safety of a
conventional car with the small road footprint and high efficiency of a
motorcycle. The project comprised nine industrial companies and
academic institutions from across Europe who collaborated to prove the
concept. The project resulted in the construction of five prototypes:
three were used for crash testing, one was used for chassis
development, and one was a show vehicle.
This thesis focuses on the design,
development and testing of the novel tilting system that was the focus
of the research at the University of Bath. The role of the chassis of
CLEVER is to provide safe and predictable handling while satisfying the
requirements of the project. Due to the narrow wheel track, the CLEVER
vehicle needs to bank into corners in a similar manner to a motorcycle
to maintain stability. The requirement of car-like controls
necessitates an active, automatic tilting system.
The two primary components of the
tilting chassis are an active control system, which controls an
actuation system that performs the tilting action. While previous work
includes modelling and simulation of active control systems, none have
taken the steps to develop an actuation system with which to tilt a
vehicle, and none have developed a system appropriate for a serious
means of transport. Through evaluation and assessment of simulation and
modelling work for both the active control system and the hydraulic
actuation system, the tilting system was developed. Following detailed
design work of the chassis systems, a development prototype was
constructed, including the implementation of the tilting system in
hardware. The vehicle achieves the targets of the project with the
results showing an acceptable correlation with the simulation
work.
It is proved that a tilting
three-wheeled vehicle with one front wheel and a cabin that tilts,
which uses direct tilt control as its tilting strategy, can achieve a
balanced cornering condition. Good results for steady state handling
were achieved, however, as predicted in the simulation work, transient
performance is limited. A high control gain value required to provide
fast response also increases the moment applied between the upright
rear unit and the tilting cabin. Aggressive steering inputs from the
driver allows the vehicle to generate cornering force significantly
before the tilting system reaches the balanced point, leading to a
dangerous condition and possible rollover.
While the CLEVER vehicle offers a
tangible glimpse of an alternative vehicle concept, which has achieved
very positive public attention, further work, including the
investigation of alternative control strategies and more sophisticated
control, is required to enable the concept to succeed.
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The Application of Self-learning to Injection Moulding Machines
Centre for Power Transmission and Motion Control
University of Bath, Bath, UK
Production of quality injection moulded parts is a complex task that
requires a deep understanding of the interaction between machine
settings and in-mould parameters. This project reports on the
monitoring of the polymer dynamics during the injection cycle and
proposes an effective control scheme for the process. The
study is focused on an Arburg 25-tonne injection moulding machine which
is hydraulically-actuated. For the modelling and simulation of the
filling and packing phases, the dynamics of both the machine's
hydraulic circuit and the polymer (polypropylene) behaviour were
investigated. The simulations were validated on a modified version of
the injection moulding machine in which a specially instrumented mould
was used.
To assess the extent of solidification
of the part and identify phase changes during the cycle, two monitoring
methods were studied. One makes use of ultrasound transducers while the
other utilizes fast-response thermocouples. Both methods were found to
enhance the control of the process. The ultrasound feedback provided
sufficient information for quick set up of the controller in real
time.
A hybrid minimal controller synthesis
(MCS) controller was developed and evaluated experimentally for the
closed-loop control of flow and pressure trajectories. The algorithm
does not require a priori information about the plant dynamics. To
reduce the MCS sensitivity to noise in the feedback signals, a
modification of the MCS is proposed and validated. This approach is
shown to enhance the performance of the machine.
A major disadvantage in conventional
moulding is the difficulty in influencing the molecular orientation at
the core. Vibration of the melt polymer has been applied by previous
researchers, by means of additional injection cylinders, because
control of fast-acting screw dynamics could not be achieved with
conventional control methods. A new method is proposed here, where
vibration of the screw in a conventional moulding machine is controlled
by the hybrid MCS algorithm.
The mechanical properties of tensile
specimens produced with vibration were compared with parts produced by
conventional moulding. They show significant improvements; part warpage
is reduced by up to 30% and tensile modulus is increased by around 10%.
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The Utilization of Mathematical Model of Dynamical Properties
of Hydrostatic Drive as a Diagnostic Tool
Department of Hydraulic Machinery Faculty of Mechanical
Engineering
Slovak University of Technology, Bratislava, Slovakia
This thesis deals with the design of technical diagnostic method which
uses for this purpose dynamical model of diagnosed object (in this
case, the research was focused on diagnostics of hydrostatic drive).
Therefore this thesis had the following main aims. The first aim was to
design the mathematical model of hydrostatic drive and its dynamical
properties. The second aim was to design and to test the first step of
developing diagnostic method.
The final mathematical model of hydrostatic drive dynamical properties
was created with the following approach. At first were created partial
models of all hydrostatic drive components. These partial models were
obtained upon the mathematic-physical analysis and experimental
identification approach. Final mathematical model was created by the
synthesis of mentioned partial models.
Within the design of technical diagnostic method was developed
procedure that describes single stages of its realization. This
procedure is based on comparing and following analysis of time
responses of selected output signals (speed of hydrostatic motor shaft
- nM, torque on shaft of displacement pump - MG) obtained from
simulations (reference technical state) and time responses of output
signals measured on diagnosed object. Further was realized analysis of
constructional junctions that can be diagnosed by developing method,
and next were determined diagnostic parameters (KQSG, KQSM, KMSG, KMSM)
which directly indicate the change in technical state and the rate of
this change with respect to reference state. Further more was chosen
the test failure for testing of developing method. In this case was
chosen test failure in the form of relative wearing of sliding pair:
supporting disc (LD) – valve plate (RK) situated in
displacement pump. Progress of the wearing was simulated with
installation of various pairs LD-RK that represent single states of
displacement pump wearing. Finally was realized the test of developing
method for chosen failure. For the purpose of determining of
K-parameters values was used approach of experimental identification.
The obtained results show that the developing method of technical
diagnostics is suitable for detecting of failures which have relation
with changing of volumetric and torque losses. Further results show
that the change of volumetric losses is more sensitive to change of
technical state than torque losses. Following this the KQS parameters
are the most suitable diagnostic parameters for the observing and
quantification of technical state changes (in this case of testing
failure).
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Simulation of the Lock’s Fluid Power System and its
Utilization in Prognosis of System’s Condition
Department of Hydraulic Machinery, Faculty of Mechanical
Engineering
Slovak University of Technology, Bratislava, Slovakia
This thesis deals with methodology of using
simulation model for
condition monitoring purpose especially for prognosis. The system under
study was hydraulic system controlling the down gate of the lock at the
Gabcikovo dam. Presented prognosis method helps to make effective
maintenance plan on the facility, where every maintenance operation
should be carefully scheduled due to the importance of the systems
functionality, which ensures continuous transport on the Danube
river.
Measurements
and simulations were periodically compared. By this way, values of
monitored parameters were defined and recorded during the periods of
system operation. This procedure can also detect and locate beginning
failures or wear of the components. The focus was on the parameters
like cylinder leakage coefficients, coefficient of viscous friction in
cylinder and in check-q- meters, the gap between bore and the spool in
the pilot operated proportional directional valves.
Acquired
parameters data from simulations and measurements together with
historical data of system behaviour were inputs to the wear prediction.
Recorded historical data contains of the information about past
failures, their reasons and occurrences calculated per year. The
artificial neural networks were chosen to be forecasting tool in this
work. The experiments were done with feedforward neural networks
trained in supervised style with back – propagation
algorithm. The most
feasible results were obtained using three or four layered networks
trained using Levenberg – Marquardt algorithm. Due to the
complicated
maintenance and the high cost of the hydraulic cylinder at this
facility the trend of the internal leakage coefficient and external
leakage coefficient of the hydraulic cylinder has been predicted.
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Simulation of the Lock’s Fluid Power System and its
Utilization in Prognosis of System’s Condition
Department of Hydraulic Machinery, Faculty of Mechanical
Engineering
Slovak University of Technology, Bratislava, Slovakia
This
thesis deals with methodology of using simulation model for condition
monitoring purpose especially for prognosis. The system under study was
hydraulic system controlling the down gate of the lock at the Gabcikovo
dam. Presented prognosis method helps to make effective maintenance
plan on the facility, where every maintenance operation should be
carefully scheduled due to the importance of the systems functionality,
which ensures continuous transport on the Danube river.
Measurements
and simulations were periodically compared. By this way, values of
monitored parameters were defined and recorded during the periods of
system operation. This procedure can also detect and locate beginning
failures or wear of the components. The focus was on the parameters
like cylinder leakage coefficients, coefficient of viscous friction in
cylinder and in check-q- meters, the gap between bore and the spool in
the pilot operated proportional directional valves.
Acquired
parameters data from simulations and measurements together with
historical data of system behaviour were inputs to the wear prediction.
Recorded historical data contains of the information about past
failures, their reasons and occurrences calculated per year. The
artificial neural networks were chosen to be forecasting tool in this
work. The experiments were done with feedforward neural networks
trained in supervised style with back – propagation
algorithm. The most
feasible results were obtained using three or four layered networks
trained using Levenberg – Marquardt algorithm. Due to the
complicated
maintenance and the high cost of the hydraulic cylinder at this
facility the trend of the internal leakage coefficient and external
leakage coefficient of the hydraulic cylinder has been predicted.
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A Study on Improving Control Performance of Hydraulic Motor
Rotary Drive Systems using Neural Networks
Department of Control Systems
Tokyo Institute of Technology, Tokyo, Japan
Hydraulic motors
controlled by servo valves are widely utilized as position and velocity
servo control systems in all kinds of industrial and vehicle fields
because of their high power density and quick response. However, it is
generally not easy to achieve high control performance in hydraulic
motor systems since they have a large nonlinearity, such as the dead
zone, which is originally caused by leakage and friction. In recent
years, numerous studies have been conducted to improve the nonlinearity
of hydraulic motor systems by introducing various control algorithms. A
Neural Network can be considered as an effective controller because it
is capable of flexible learning and mapping for nonlinear
characteristics. The objective of this study is to attain precise
position and velocity control accuracy by employing a state feedback
Neural Network controller in a hydraulic motor system with an
undesirable dead zone. In the proposed system, the Neural Network
control system is constructed by the following process. At first, a
state feedback controller is designed based on a nominal model of the
hydraulic motor system; subsequently, the I/O characteristics of the
designed controller are mapped to the Neural Network by offline
training. Then, the Neural Network controller is incorporated into the
feedback loop of the system. In this system, the desirable output of
the hydraulic motor is obtained by the online training of the Neural
Network to minimize the error between the reference model output and
the hydraulic motor output. Simulation and an experiment were conducted
in various conditions, and from the results, it was confirmed that the
positioning accuracy, low speed driving performance, and velocity
control performance was considerably improved. Finally, the
effectiveness of the proposed Neural Network control system for
improving the performance of hydraulic motor systems was clarified.
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Electro-Hydraulic Control System of Automobile Power Train
Department of Mechanical Systems Engineering
Yokohama National University, Kanagawa, Japan
This paper describes electro-hydraulic control systems for an
automobile power train, where the research aim is to gain high
responsibility and reliability of newly developed devices, an
electro-hydraulic valve actuator for cam-less engines and a
6-power-roller half-toroidal continuously variable transmission (CVT).
In recent years, two types of variable valve actuators for a
cam-less engine, electromagnetic and electro-hydraulic, have been
developed. However, there are some issues of these actuators to attain
reliable control on valve landing-velocity deceleration without any
electronic position sensors. From this point of view, the former
actuator is not so strong against gas-pressure change, while the latter
has issues of power waste and valve speed. As freedom degree for
variable control of combustion ratio is more required for the targeted
medium-speed diesel engine, the electro-hydraulic type was chosen. The
first prototype of a sensor-less electro-hydraulic valve actuator
(EHVA) with a hydro-mechanical position feedback mechanism was
controlled using a two-port switching valve. It operated in 24 ms for
full stroke of 12 mm. This paper presents two speed-up trials for
working at 2100 rpm in engine speed, in 19 ms of total valve
opening/closing time, one is applying a three-port switching valve
instead of the two-port valve and the other is use of multi-pulse
control. A bond graphs simulation program optimized the parameters of
the EHVA and the newly modified actuator succeeded to complete the
valve lift motion within 19 ms at full stroke. A CVT that maintains the
engine in its optimum power range has the potential to solve two issues
of fuel economy and tail-pipe emissions. In 1999, a traction-drive
half-toroidal CVT was commercialized for a large-displacement engine in
front-engine rear-drive vehicle. In this paper, experiments on a
prototype confirmed the possibility of a six-power-roller variator
developed for the purpose of further increasing transmission torque
capacity up to 430 Nm as opposed to a current four-power-roller, and
further simplifying the speed-ratio control system. Technical
advancements include: confirmation of synchronization and stability of
six power rollers; establishment of a cost-effective speed-ratio
control system using a small three-port electro-hydraulic pressure
proportional valve; replacement of the hydro-mechanical servomechanism
with a simplified sensorless control system.
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Research and Modeling of Fluid Flow in a Hydrodynamic Coupling
Department of Hydromechanics and Hydraulic Equipment
Faculty of Mechanical Engineering
VSB-Technical University of Ostrava, Ostrava, Czech Republic
This dissertation deals
with the investigation of the fluid flow inside operating area of the
hydrodynamic coupling. Two approaches were applied, i.e. numerical
modelling by means of finite volume method in CFD program Fluent, and
experimental measurement to verify the obtained results. In this
respect the main task was to assemble coupling test facility for
measuring of the secondary characteristic fields and definition of the
mathematical model, i.e. verification of the sliding mesh technique
applicability and selection of suitable turbulence and multiphase
model. As a first step due to the time demandingness of the
computation, numerical model was tested on a simplified model of the
hydrodynamic coupling, where the main parameters were determined in
accordance with literature for selected transmitting power and
rotational speed of the engine. Findings gained on this simplified
model of the coupling helped as a basis for computation on the model of
the real hydrodynamic coupling HS 30 sequentially. Then it was possible
to compare values of the torque at a given slip and a fill level
obtained by the numerical simulation with the corresponding
experimental values on a relevant secondary characteristic field and
together with the values calculated according the one-dimensional
stream theory. At the end the modelling of the run up of inactive
turbine wheel by the hydrodynamic effect of the working fluid at the
jump unloading torque change of inactive turbine wheel are described in
this work and results are again verified by the experiment.
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Books & Proceedings Published in 2007
ISBN:
978-86-86663-15-3
This university book, written in Serbian (Latin),
systematises basic theoretical principles and analytical methods that
are used in hydraulic component and system design and performance
prediction. In detail solved and explained work examples follow every
chapter, so the book is suitable for students, researchers and
practicing engineers in academia and in industry. The book has eight
chapters: Physical Concepts of Fluid Power Hydraulics, Hydraulic
Machinery – Pumps and Motors, Hydraulic Machinery –
Cylinders and Rotary Actuators, Application of Orifices in Hydraulic
Components and Systems, Directional Control Valves, Pressure and Flow
Control Valves, Hydro-accumulators and Additional Components, and three
appendixes: SI prefixes, Unit Conversion and SI Symbols.
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