This thesis focuses on how to improve design and development of complex engineering systems by employing simulation and optimization techniques. Within the thesis, methods are developed and applied to systems that combine mechanical, hydraulical and electrical subsystems, so-called multi-domain systems.
The usage of simulation and optimization in engineering design is gaining wider acceptance in all leads of industry as the computational capabilities of computers increase. Therefore, the applications for numerical optimization have increased dramatically. A great part of the design process is and will always be intuitive. Analytical techniques as well as numerical optimization could however be of great value and can permit vast improvements in design.
Within the thesis, a framework is presented in which modelling and simulation are employed to predict the performance of a design. Additionally, non-gradient optimization techniques are coupled to the simulation models to automate the search for the best design.
Most engineering design problems consist of several often conflicting objectives. In many cases, the multiple objectives are aggregated into one single objective function. Optimization is then conducted with one optimal design as the result. The result is then strongly dependent on how the objectives are aggregated. Here a method is presented in which the Design Structure Matrix and the relationship matrix from the House of Quality method are applied to support the formulation of the objective function.
Another approach to tackle multi-objective design problems is to employ the concept of Pareto optimality. Within this thesis a new multi-objective genetic algorithm is proposed and applied to support the design of a hydraulic actuation system. The outcome from such a multi-objective optimization is a set of Pareto optimal solutions that visualize the trade-off between the competing ob-jectives. The proposed method is capable of handling a mix of continuous design variables and discrete selections of individual components from catalogs or databases.
In real-world situations, system parameters will always include variations to some extent, ant this fact is likely to influence the performance of the system. Therefore we need to answer not only the question "What is best?", but also "What is most robust?". Within this thesis, several approaches to handle these two different questions are presented.
This thesis deals with modelling and simulation applied to mobile hydraulics. The main features of mobile hydraulics are described and the benefits of a simulation approach in research and development of mobile machinery are discussed.
Numerically efficient and easy-to-parameterisize models for mobile hydraulics components are created. This makes it possible to achieve a computationally efficient simulation model of an entire machine and the number of parameters is as low as possible. The models include all the essential functions of the components in order to carry out system level design of such machine systems. The pump system model consists of a variable displacement pump including LS-regulator and power restrictor. The loss model is based on the Dorey model and the identification is made semi-empirically with a reduced number of parameters. The mobile valve model includes semi-empirical sub-models of the main valve spool, pressure compensator/flow sharing compensator, load drop check valve, anti-cavitation valves and shock valves. An empirical model for an oil cooler and polynomial fit for passive heat transmission of the machine are also suggested.
A method for defining mobile valve dynamics without performing measurements is introduced and verified against the mobile valve used in the example machine system.
The simulation software implementation and the advantages of the approach are presented. As a result, an engineering tool for R&D operations is created. An actual company-based R&D case demonstrates the application. Simulation study of a forest machine dealing with machine energy efficiency is carried out.
Streamline coordinate systems are effective for solving the flow inside the channel with curved solid walls and the flow with free surfaces. In this thesis, a new numerical method is put forward to solve the governing equations in the streamline coordinate system. Two examples are computed using the method and the validity is confirmed by comparing the numerical results with the previous experimental results. As the first example, the flows in conical poppet valve are computed. The pressure distributions on the poppet and on the chamfered seat, the axial force acting on the poppet and the normalized flow rate are discussed. The second example is the jet from a coaxial pipe.
Performance and environmental demands as well as demands on customisability on engineering systems have led to an increasing usage of embedded software. The software provides the possibility to make the most out of the system in each situation but also leads to a tighter coupling between all subsystems. The latter has the effect that every subsystem needs to be taken into account when predictions of system performance are performed. Due to the increased complexity of systems, several engineering domains are part of the product development process. In the thesis the domains of hydraulics and mechanics are of special interest. A single domain is seldom fitted to handle the design issues of complex systems, rather collaborative efforts are necessary. The main question in the thesis is how simulation best can support engineering teams in their struggle to design the "best" system, taking into account limitations in time and resources.
Simulation models are the bases for any simulation. Choice between modelling formalisms, tools and model architecture is a necessary first step. There is a lack of knowledge both within industry and academia about the available choices. This has led to an inefficient use of the knowledge of the personnel as well as usage of tools that are less suitable for the application. Although standardization may in the long run form a bases for efficient multi-domain modelling there is a need for methods that make use of present resources and that are prepared for upcoming changes in the area of modelling.
As an input to the simulation phase, a number of models exist, possibly in different tools. As in the modelling phase, there are several options for simulating the total systems. Either the models are kept in their native tools and multi-domain simulation is performed or they are exported to some tool containing a good numerical solver. The pros and cons of these alternatives are discussed. It is shown how to maintain a stable and fast simulation in the first case, something that is not normally addressed in commercial solutions.
In simulation of complex systems it can often be difficult to interpret the result. In this thesis an approach to trace and record the events in the system is presented, that has the potential of disclosing cause-effect relations in the system to the user.
The geometric analysis and accuracy enhancement of parallel topology robots is of theoretical interest as well as having potential for the application in industrial settings where parallel robots are used for tasks in which positional accuracy is important. This work presents new techniques for modelling of closed loop mechanisms and applies these experimentally in the calibration of a real parallel topology robot: The Delta robot. This work extends the current literature on serial robot calibration into the realm of parallel robots and presents a systematic approach which does not require the model or solution technique to be adjusted for the particular geometry of the robot under investigation.
The geometric modelling technique is quite general although in its current implementation it is only capable of modelling mechanisms that have rotary joints. Theory is presented for modelling of prismatic joints and the model can be adapted to handle joints of any type. The model analyses the structure as if it were a tree of bodies, each connected by a rotary or prismatic joint. A method of calculating the derivatives of the body frame positions with respect to the geometric parameters is also given.
A defining characteristic of parallel topology mechanisms is that the kinematic chains form closed loops. Finding the joint configuration that has all loops properly closed is a non-linear minimization problem referred to as the closure problem. This is solved using the Levenberg-Marquardt technique.
For analysis of errors in a robot that is already assembled, an experimental calibration procedure is necessary. This procedure compares measured endpoint positions with those predicted by the geometric model and attempts to find a set of parameters that minimizes these differences. The calibration procedure that was developed was tested on a number of simulated robots and a working Delta robot, which was designed and built specially for the calibration experiment. The mechanical design of the robot, software and hardware design of the robot controller, and the software implementation of the modelling and calibration procedures are described.
It was found that the modelling, identification, and the implementation methods worked successfully on the robots examined, but that the implementation process was too slow for use in a practical controller because of the need to perform multiple direct geometric solutions. The computational effort required for the implementation procedure was considerable, but use of a compiled computer language and optimized code would provide significant improvement.
The aim of the study was to find methods to improve the energy efficiency of hydraulic closed-loop controlled heavy-duty hydraulic manipulators. Fast response but still energy-efficient motion control of hydraulic manipulators is still a formidable problem due to the complexity of the hydraulics. Fast response hydraulics are usually characterized by high-energy losses and on the other hand energy-efficient control systems by slow response and stability problems.
In this study, an energy-efficient motion control system with the fast response is proposed, designed and implemented. The proposed motion control consists of four interconnected subsystems that are: a model-based Computer Torque/Force Controller, force controlled hydraulic drives, a hydraulic power unit controller and trajectory generator.
The main contribution of this thesis falls into the area of system design, and especially design of systems that involve several engineering domains, so-called multi domain or heterogeneous systems. The design of these systems is concerned with a need for efficient tools, especially in the early conceptual phase of the development process.
The scope of this work is heterogeneous systems and hydraulic systems for automotive engines, and gasoline engines in particular. To date the use of such systems in automotive engines has been restricted to a small number of applications, predominantly lubrication systems. Lubrication systems have very much in common with traditional fluid power systems, with the major difference that the power in form of pressure and flow is used in order to transport a lubricant and not for actuation purposes. Temperature aspects as they are treated in this thesis are significant for lubrication system design in combustion engines, as the oil is used both for lubrication and cooling.
Another application area for hydraulic systems in vehicle engines is camless valve trains, where the inlet and exhaust valves of the engine is operated by hydraulic means. In this manner the losses which arise due to gas exchange can be significantly reduced. Such a variable valve train system is proposed in this thesis, where power consumption and robust operation are put in the foreground. In the design of new system concepts there are usual some critical components where the performance has to be verified at an early design stage. In the case of the valve train system proposed, both the hydraulic switching and check valves prove to be key components. System design implicates validated component models which made in-depth modelling and model identification issues to the cornerstones of this work.
This thesis discusses numerical simulation and optimization techniques, both as analysis and design tools for automotive engine systems. In the case of simulation based optimization, an optimization strategy is used in order to vary a set of design parameters in order to satisfy an objective function. The formulation of this objective function is obviously crucial for the optimization output. In this thesis guidelines for the creation of such a goal function are given where the involvement of the design team has been considered important.
The main aim of the interdisciplinary work is presentation of rational and effective methods of data acquisition and data processing, connected with investigations of hydraulic drive systems (HDS). Topics involve selected problems of data acquisition and analysis, considered under assumptions about limitations and criteria of instrumentation and measurement method choice. The common measurement processes characteristics and processing models, related to structure of the measurement system of the investigated HDS are provided with author's proposals concerned with system quality and with original, representative simulating models. Considerations and conclusions are based on procedures and results of the real experiments as well as on computer simulations results, carrying out on particular elements of - and on the whole HDS. Procedures and algorithms presented in the work can be applied to optimization of measurement system designed for investigations or diagnostics of e.g. heavy duty machines, basing on computer simulation.
In this thesis a concept for semi-active aircraft landing gear systems controlled by fuzzy-logic is developed and the potential improvements on the landing gear and aircraft dynamics are investigated. It is shown that by semi-active landing gear systems the maximum structural loads induced by the touchdown impact can be significantly reduced and the passenger comfort on the rough runways can be considerably improved.
This study considers some possibilities of CFD application in hydraulics. Design of hydraulic valves is a wide potential area for application of CFD, especially in respect of calculation of flow forces. These flow forces should be minimized during the optimization and also determinable for a given pressure difference or volume flow.
Within the scope of this study some valve geometry were examined with respect to flow forces using CFD calculations. At first a conventional slide valve was calculated and detailed error analysis of CFD calculations of cavitating interior flow through valves were performed. Sequentially a compensated seated valve was calculated using two commercial CFD codes and two turbulence models. Finally a new unconventional valve geometry was examined and optimized with the aim to confirm the results of the error analysis previously carried out. The interior non-cavitating flow through this valve geometry was examined experimentally and theoretically using CFD.
The thesis handles one hydraulic free piston engine design, its features and Performance dependence on design parameters. A hydraulic free piston engine, HFPE, combines a combustion engine and a hydraulic pump into one compact component, which has only one linearly moving part, the piston assembly. The piston assembly motion is not restricted by any mechanical linkages and therefore compression control is possible. When the piston assembly moves linearly back and forth between left and right extremes by means of fuel energy, its hydraulic pistons produce direct hydraulic energy. Because of its simple design, higher power density and lower manufacturing costs than those of a conventional engine-pump combination are achieved. On the other hand, the piston motion requires more active and complicated control system than in crankshaft engines.
The object of this thesis was to analyze and illustrate the potential of one hydraulic free piston engine design, the dual piston HFPE. Other major projects in which hydraulic free piston engines are developed are also introduced. The thesis includes analytical, simulation and experimental studies of the studied engine concept. The analytical study is used to define the effects of design parameters on the performance variables. Simulation study is also performed, because the analytical study can not take account all the dynamic effects and operational variables. The prototype engine was built and the experimental test results of the prototype engine are shown and the observed features and difficulties of the engine are discussed.
The knowledge of the operation and ageing behaviour of ecologically acceptable hydraulic fluids is a prerequisite for successful applications of these fluids in hydraulic systems, in particular in the area of mobile hydraulic with its high power density. This thesis presents extensive investigations which were performed in laboratory as well as in the test field using different kinds of ecologically acceptable hydraulic fluids. The investigations indicate that the ageing processes of ecologically acceptable fluids are influenced by many parameters. Some starting points for the improvement of these fluids are discussed as well as the possibilities for an optimized design of hydraulic systems.
In this thesis, applications of numerical simulation of the non-isothermal turbulent flow is reported as a tool to investigate the flow in the atmospheric boundary layer. To describe the atmospheric flow, Navier-Stokes equations, or Reynolds averaged equations can be used together with other conservation equations written for mass, energy and scalar quantities. The set of partial differential equations is solved using the numerical methods. Statistical turbulence models such as k-e, RNG k- e or Reynolds stress model can be applied. New approach to turbulence modelling -Large Eddy Simulation- can be used to obtain more insight in the structure and physics of the convective boundary layer.
In this work application of general computational fluid dynamics (CFD) code Fluent in the field of atmospheric turbulence modelling has been studied. Physical model, turbulence models including LES have been tested together with boundary conditions, solution parameters, computational grid. Definition of the source terms in the equation written for turbulent kinetic energy and dissipation rate was tested, which is of great importance for the plume dispersion modelling.
Journal Bearing Performance in Gear Pumps
Marius Gutes (Technical University of Barcelona, Spain)
Proc. of 1st FPNI - PhD Symposium Hamburg 2000, pp. 259-269
Development of a Hydraulic Master-Slave System for Tele-Robotics
Shigeki Kudomi (Gifu University, Japan)
Proc. of 1st FPNI - PhD Symposium Hamburg 2000, pp. 467-474
Edited by: J. L. Johnson
545 pages
Publisher: IDAS Engineering Inc.
ISBN 0970225903
This comprehensive reference book contains hundreds of figures and formulas that will instruct and aid the reader in the application of electrohydraulic technology to design of hydraulic systems. 20 chapters deal with basics of hydraulic circuit analysis, valve characteristics and performance, pump and motor modelling, optimal system sizing, hydromechanical resonance, frequency response, closed loop positioning systems, motion control methods and common electronic interfaces and signal conditioners. Principles are driven home through scores of fully worked example problems rather than arcane theoretical discourse.
Edited by: R. B. Walters
344 pages
Publisher: Kluwer Academic Publishers
ISBN 0-7923-6537-2
The book essentially studies and analyses force and motion control systems, from simple hydraulic to complex electro-hydraulic control systems, bridges the gap in knowledge between the control engineer and the practical hydraulic application engineer, and provides a contribution towards the wider application of hydraulic systems.
This second enlarged hardbound edition includes an entirely new addition - a tutor for the application of Hydro Analyst. The tutor provides a hands-on system simulation procedure for the system modelling package Hydro Analyst supplied with this edition as a floppy disk. The package contains an extensive component database and comprehensive graphics facilities.
This book is essential reading for engineers working in hydraulics and control.