PhD-Theses completed in 2007
Analysis of fluid ageing and methods to predict the ageing
behavior of environmentally compatible lubricants in new
developed tribological systems
Institute for Fluid Power Drives and Controls
Aachen University, Aachen, Germany
Tribological
contacts provide a basis for various mechanical systems and processes.
Their optimum performance determines the lifetime of the system as well
as its efficiency. Due to this lubricants within these systems are of
great importance. If functions of the lubricants are
transferred into the surfaces of the friction partners, which is the
idea of the collaborative research center 442, more attention has to be
drawn to the ageing stability of the lubricant.
This is the background for this work. Starting with a general
description of the chemical ageing mechanisms, this work evaluates the
influence of the chemical composition of newly developed lubricants on
the ageing properties. To analyze the impact of friction on the ageing
behavior a new ageing tests has been developed. Based on the rotating
pressure vessel test the new test set up contains a disc on disc
tribometer. The results show an influence on the ageing even when
considering the extra amount of energy which is brought into the
system.
An ageing simulation to predict the
lifetime of the fluid in the hydraulic system has been set up. The
simple loads of standard ageing tests on model scale become complex
when real systems have to be considered. Characteristic values are used
to summarize these loads and form input values for a neural network.
This network computes the change in the fluid’s properties
due to the load. Taking this route the change of properties can be
calculated as a function of time. By use of test rig runs the neural
network is trained. A comparison between the measured and simulated
change in viscosity proves the concept.
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Guo Guanzhu
Design and Manufacture for Strong Shear Rheometer and
Experimental Study of Shear Flow Cavitation
The State Key Laboratory of Fluid Power Transmission and
Control
Zhejiang University, Hangzhou, China
The research on design and manufacture for strong shear rheometer and
experimental of shear flow cavitation is the main objective of the
thesis. Base on the techniques of high-precision designing and
machining, a new Couette apparatus where its outer cylinder rotating
with flow visualization and pressure control has been made. The
transient computed temperature was consistent with the experimental
temperature. It shows that the shearing torque and the symmetrical gap
and the transient temperature of this apparatus are precise. Overcoming
some drawbacks of previous methods measuring gas-solubility, a new
piston apparatus was established in which the state equation of ideal
gas is used to determine the amount of gas-dissolution. An expression
of the Bunsen solubility of air in 500cSt silicone at temperature of
293.2 and 353.2 K and in the gas-pressure range of 0-350 kPa has been
determined. The Bunsen solubility and gas-pressure exhibit good
linearity while the relationship between the molar fraction and the
pressure in the experimental range is nonlinear but can be well fitted
by the Krichevsky-Ilinskaya equation. Considering influence of liquid
surface tension, equilibrium of a spherical nucleus has been discussed
based on mechanical equilibrium of the interface. We analyzed the
thermal behavior of the gas content. Gas diffusion and nucleus
stability has been discussed based on diffusive equilibrium of the
interface. The strong shear rheometer has been used in the cavitation
inception experiment after the saturation ratio of air has been
changed. We had given an empirical relationship between the saturation
ratio and Peclet number and the Capillary number and the cavitation
index. We found that critical shear stress of cavitation inception is
roughly proportional to the applied pressure, but it is less than
results of PNSCC. The critical shear stress of cavitation inception is
roughly inversely proportional to the saturation.
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Technical Research on In-situ Detection for Deep-sea
Hydrothermal Fluid and Its Integration of Prototype System
The State Key Laboratory of Fluid Power Transmission and
Control
Zhejiang University, Hangzhou, China
The dissertation has carried out the research on in-situ detections of
temperature and pH value for deep-sea hydrothermal fluid, and therefore
an in-situ multipoint temperature measurement system and a long-term
in-situ pH value detection system for deep-sea hydrothermal fluid have
been developed respectively. In-situ multipoint temperature measurement
system can acquire the temperature parameter during the form of
hydrothermal chimney; long-term in-situ pH value detection system can
implement long-term insitu pH value detection for deep-sea hydrothermal
fluid. Owing to pH detection electrode can not implement long-time pH
value detection in deep-sea hydrothermal fluid environment, the
technical measures of implementing self-calibration of pH detection
electrode using deep-sea fluid control technology has been put forward
in the dissertation. In order to solve high pressure-resisting problem
in deep-sea fluid control technology, a kind of fluid control system
which could adapt the pressure variety in deep-sea high pressure
environment was designed using pressure compensation method. For the
implement process of two in-situ detection systems for deep-sea
hydrothermal fluid, technologies of mechatronic integration about two
systems have been studied comprehensively. In order to validate the
reliability of two in-situ detection systems, finally, sea trials of
two systems have been introduced.
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Design of a Free-Piston Stirling Engine-Pump
Department of Mechanical Engineering
University of Wisconsin-Madison, Wisconsin, USA
A free-piston Stirling engine- pump
(FPSEP) combines a Stirling cycle that provides power to an integral
hydraulic pump. Stirling cycle engines offer potential advantages over
internal combustion engines in fuel choice, quietness, and emissions. A
Stirling-cycle, free-piston engine-pump has been investigated for use
in human-scale, fractional horsepower applications and information.
A design has been developed that combines a free-piston
Stirling engine with a single-piston pump, check-valves, and pressure
relief valve. The Stirling engine prototype utilizes a pneumatic
cylinder to actuate the displacer and thus control engine speed. Heat
is supplied to the engine by an electric heater and cooling is provided
by chilled water. The pump portion of the engine-pump consists of one
single-acting piston with appropriate valve system for pumping fluid.
The connecting linkage between the engine piston and the pump piston
provides allowance for misalignment. In the proof-of-concept device,
pressures, temperatures, positions and velocity are measured.
The
performance and dynamic characteristics of the free-piston Stirling
engine-pump have been simulated to determine its operating
characteristics over a wide range of conditions. The simulation results
indicate that a FPSEP operating at 550 psi (3.8 MPa) working pressure
and with an engine displacement of 1.5 in3 (24.8 cm3) could produce 1.8
HP (1.3 kW) when operating at 4400 cycles per minute.
A
free-piston Stirling engine-pump prototype has been built and tested.
The ultimate gas working pressure of the prototype was 3.4 MPa (500
psi). The device was hydrostatically tested to this value. A beating
phenomenon occurred during engine testing with forcing frequency of 5
Hz. For that reason, this prototype also has a speed limit for the
displacer actuated by a pneumatic cylinder. The experimental results
revealed that this engine without, insulation, using air and nitrogen
as a working gas at a pressure of 0.69 MPa (100 psi) and 1.72 MPa (250
psi), provided significantly lower power than the simulation predicted.
Because of hardware limitations desired operating temperature and
pressure could not be achieved. Additionally, more friction and heat
loss
lead to less power output than the simulation predicted.
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PhD-Theses completed in 2008
Flow Pulsations in Fluid
Power Machines – a Measurement and Simulation Study
Division of Fluid and Mechanical Engineering Systems
Linköping University, Linköping, Sweden
Stricter requirements for better working environment involve noise and
vibration control of hydraulic machines. The operational conditions for
hydraulic machines, such as pressure and rotational speed, are also
increasing and this makes it even more difficult to develop a quiet,
vibration-free machine due to the interdependence between noise and
escalating operating conditions. The thesis investigates machines
working in different driving modes and under different operational
conditions. A so-called cross-angle is proposed for motor as well as
pump/motor applications with variable displacement angles. The
cross-angle is intended to reduce the overall noise level in the
machines working area. Other noise reduction features are also
considered for machines working in different modes.
To facilitate the system integrator’s ability to design quiet
systems, methods to determine the source flow and source impedance of
the machine are essential. The source flow is assumed to be created at
the valve plate and the internal impedance related to the high pressure
port are completely independent of the rest of the system. Knowledge of
these properties makes it possible to foresee the noise properties of a
system already on the design phase. A novel source flow measurement
method, the source admittance method, is investigated here. The method
is considered to be robust and easy to use to suit industry
requirements.
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Saving Energy in Construction Machinery using Displacement
Control Hydraulics –
Concept Realization and Validation
Division of Fluid and Mechanical Engineering Systems
Linköping University, Linköping, Sweden
In the sector of mobile hydraulics, valve
controlled systems are predominant. In these systems the load force and
speed are ad-justed by control valves. In machines where multiple
drivers are used in parallel at extremely varying loads the energy
efficiency of such systems is often compromised over large working
regions. Most valve controlled systems also lack the possibility to
recuperate potential energy.
A
different category of hydraulic systems, called displacement controlled
hydraulics are based on the manipulation of the hydraulic flow
using the relative displacement of the hydraulic machines as the final
control element. This type of hydrostatic power transfer yields a
resistance free velocity control, ideally leading to lossless load
actuation.
This
thesis concerns the introduction of a new type of displacement
controlled hydraulic system, adapted for construction machinery.The
system decouples the hydraulic functions using one dedicated hydraulic
machine for each drive. These machines are of open circuit type,
capable of over centre operation which enables energy recuperation. The
system also comprises four separate valves that by means of switching
allow the cylinder to be controlled over all four load quadrants.
Depending on the selected valve hardware, the system may also
include features available in a conventional valve controlled system,
such as meter-out flow control. The system supports both symmetrical
and asymmetrical cylinders. However, using the asymmetrical type the
load may be controlled in two distinct states of operation. This yields
an increased region of operation, which is otherwise generally stated
as a drawback in displacement controlled systems. It also allows the
selection between different control modes, where one of the modes is
always more efficient than another.
In this research both theoretical studies and a practical
implementation demonstrate the energy related benefits of the new
concept. The target application of this study is a medium-size wheel
loader. Measurement results using the wheel loader in a short truck
loading cycle show a 10 % reduction in fuel consumption. According to
the theoretical investigation, this corresponds to a 20 % reduction in
energy consumption for the hydraulic system itself.
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Fluid Power Applications Using Self-Organising Maps in
Condition Monitoring
Division of Fluid and Mechanical Engineering Systems
Linköping University, Linköping, Sweden
Condition monitoring of systems and
detection of changes in the systems are of significant importance for
an automated system, whether it is for production, transport, amusement
or any other application. Although condition monitoring is already
widely used in machinery, the need for it is growing, especially as
systems become increasingly autonomous and self-contained. One of the
toughest tasks concerning embedded condition monitoring is to extract
the useful information and conclusions from the often large amount of
measured data. The use of self-organising maps, SOMs, for embedded
condition monitoring is of interest for the component manufacturer who
lacks information about how the component is to be used by the system
integrator or in what applications and load cases.
At the
same time, there is also a potential interest on the part of the system
builders. Although they know how the system is designed and will be
used, it is still hard to identify all possible failure modes. A
component does not break at all locations or in all functions
simultaneously, but rather in one, more stressed location. Where is the
location? Here, the collection of as much data as possible from the
system and then processing it with the aid of SOMs allow the system
integrators to create a map of the load on the system in its operating
conditions. This gives the system integrators a better chance to decide
where to improve the system.
Automating monitoring and analysis means not only being able to collect
prodigious amounts of measured data, but also being able to interpret
the data and transform it into useful information, e.g. conclusions
about the state of the system. However, as will be argued in this
thesis, drawing the conclusions is one thing, being able to interpret
the conclusions is another, not least concerning the credibility of the
conclusions drawn. This has proven to be particularly true for simple
mechanical systems like pneumatics in the manufacturing
industry.
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Awards in 2008
Presented at the 5th FPNI PhD
Symposium, Krakow July 2008
Awarded to
Jonathan Baker
For the paper and presentation titled
Investigation of Power Losses in the Lubricating Gap between the
Cylinder Block
and Valve Plate of Axial Piston Machines
Purdue University, USA
Awarded to
Claus Enekes
New Design of Tribological Systems of Axial Piston Pumps with Coatings
and Environmentally Friendly Fluids
Aachen University, Germany
Federica Franzoni
Developing and Tailoring a CFD Code for Multiphase Multicomponents
Flows
University of Modena & Reggio Emilia, Italy
Najoua Jouini
Valve Plate Surface Temperature Prediction in
Axial Piston Machines
Purdue University, USA
Richard Klop
Investigation of Noise Source Reduction Strategies in
Hydrostatic Transmissions
Purdue University, USA
Barbara Zardin
Modelling and Simulation of External Gear Pumps and Motors
University of Modena & Reggio Emilia, Italy
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