| 1. |
- Thore, Carl-Johan
(författare)
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Optimal Design of Neuro-Mechanical Networks
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns modeling and optimal design of Neuro-Mechanical Networks. A Neuro-Mechanical Network (NMN) can be described as an active mechanical structure, made up from a network of simple but multifunctional elements that interact with their nearest neighbors. The concept is of mechatronic character as it involves integration of actuators, sensors, signal processing, and control, into a mechanical structure. The first part of the thesis consists of three chapters. The first of these chapters contains a brief introduction to the NMN-concept and the present work. In the second chapter, the particular type of NMNs considered here is described in more detail, and the third chapter constitute a brief survey of some works relevant to optimization of active structures, including enabling technologies and static and dynamic shape control. The second part of the thesis consists of two papers, where the first paper describes optimal design of NMNs for static shape control, while the second paper is concerned with optimal design of structures that exhibit oscillatory motion.
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| 2. |
- Amadori, Kristian
(författare)
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Geometry Based Design Automation : Applied to Aircraft Modelling and Optimization
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Product development processes are continuously challenged by demands for increased efficiency. As engineering products become more and more complex, efficient tools and methods for integrated and automated design are needed throughout the development process. Multidisciplinary Design Optimization (MDO) is one promising technique that has the potential to drastically improve concurrent design. MDO frameworks combine several disciplinary models with the aim of gaining a holistic perspective of a system, while capturing the synergies between different subsystems. Among all disciplines, the geometric model is recognized as playing a key role, because it collects most of the data required to any other disciplinary analysis. In the present thesis, methodologies to enable multidisciplinary optimization in early aircraft design phases are studied. In particular, the research aims at putting the CAD geometric model in the loop. This requires the ability to automatically generate or update the geometric model, here referred to as geometry-based design automation.The thesis proposes the use of Knowledge Based Engineering (KBE) techniques to achieve design reuse and automation. In particular, so called High Level CAD templates (HLCts) are suggested to automate geometry generation and updates. HLCts can be compared to parametric LEGO® blocks containing a set of design and analysis parameters. These are produced and stored in libraries, giving engineers or a computer agent the possibility to first topologically select the templates and then modify the shape of each template parametrically.Since parameterization is central to modelling by means of HLCts, a thorough analysis of the subject is also performed. In most of the literature on MDO and KBE two recurring requirements concerning the geometrical model are expressed: the model should be flexible and robust. However, these requirements have never been properly formulated or defined. Hence, in the thesis a mathematical formulation for geometry model robustness and flexibility are proposed. These formulations ultimately allow the performance of geometric models to be precisely measured and compared.Finally, a prototyping and validation process is presented. The aim is to quickly and cost-effectively validate analytical results from an MDO process. The proposed process adopts different manufacturing techniques depending on the size and purpose of the intended prototype. In the last part of the thesis, three application examples are presented. The examples are chosen from research projects that have been carried out at Linköping University and show how the proposed theoretical results have been successfully employed in practice.
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| 3. |
- Andersson, Henric, 1963-
(författare)
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Variability and Customization of Simulator Products : A Product Line Approach in Model Based Systems Engineering
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AIRCRAFT DEVELOPERS, like other organizations within development and manufacturing, are experiencing increasing complexity in their products and growing competition in the global market. Products are built from increasingly advanced technologies and their mechanical, electronic, and software parts grow in number and become more interconnected. Different approaches are used to manage information and knowledge of products in various stages of their lifecycle."Reuse" and "Model Based Development" are two prominent trends for improving industrial development efficiency. The product line approach is used to reduce the time to create product variants by reusing components. The model based approach provides means to capture knowledge about a system in the early lifecycle stages for usage throughout its entire lifetime. It also enables structured data management as a basis for analysis, automation, and team collaboration for efficient management of large systems and families of products.This work is focused on the combination of methods and techniques within;modeling and simulation-based development, and(re)use of simulation models through the product line concept.With increasing computational performance and more efficient techniques/tools for building simulation models, the number of models increases, and their usage ranges from concept evaluation to end-user training. The activities related to model verification and validation contribute to a large part of the overall cost for development and maintenance of simulation models. The studied methodology aims to reduce the number of similar models created by different teams during design, testing, and end-user support of industrial products.Results of the work include evaluation of a configurator to customize and integrate simulation models for different types of aircraft simulators that are part of a simulator product family. Furthermore, contribution comprises results where constraints in the primary product family (aircraft) govern the configuration space of the secondary product family (simulators). Evaluation of the proposed methodology was carried out in cooperation with the simulator department for the 39 Gripen fighter aircraft at Saab Aeronautics.
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| 4. |
- Thore, Carl-Johan
(författare)
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Optimal Design of Neuro-Mechanical Networks
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many biological and artificial systems are made up from similar, relatively simple elements that interact directly with their nearest neighbors. Despite the simplicity of the individual building blocks, systems of this type, network systems, often display complex behavior — an observation which has inspired disciplines such as artificial neural networks and modular robotics. Network systems have several attractive properties, including distributed functionality, which enables robustness, and the possibility to use the same elements in different configurations. The uniformity of the elements should also facilitate development of efficient methods for system design, or even self-reconfiguration. These properties make it interesting to investigate the idea of constructing mechatronic systems based on networks of simple elements.This thesis concerns modeling and optimal design of a class of active mechanical network systems referred to as Neuro-Mechanical Networks (NMNs). To make matters concrete, a mathematical model that describes an actuated truss with an artificial recurrent neural network superimposed onto it is developed and used. A typical NMN is likely to consist of a substantial number of elements, making design of NMNs for various tasks a complex undertaking. For this reason, the use of numerical optimization methods in the design process is advocated. Application of such methods is exemplified in four appended papers that describe optimal design of NMNs which should take on static configurations or follow time-varying trajectories given certain input stimuli. The considered optimization problems are nonlinear, non-convex, and potentially large-scale, but numerical results indicate that useful designs can be obtained in practice.The last paper in the thesis deals with a solution method for optimization problems with matrix inequality constraints. The method described was developed primarily for solving optimization problems stated in some of the other appended papers, but is also applicable to other problems in control theory and structural optimization.
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| 5. |
- Braun, Robert
(författare)
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Multi-Threaded Distributed System Simulations : Using Bi-Lateral Delay Lines
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the speed increase of single-core processors keeps declining, it is important to adapt simulation software to take advantage of multi-core technology. There is a great need for simulating large-scale systems with good performance. This makes it possible to investigate how different parts of a system work together, without the need for expensive physical prototypes. For this to be useful, however, the simulations cannot take too long, because this would delay the design process. Some uses of simulation also put very high demands on simulation performance, such as real-time simulations, design optimization or Monte Carlo-based sensitivity analysis. Being able to quickly simulate large-scale models can save much time and money.The power required to cool a processor is proportional to the processor speed squared. It is therefore no longer profitable to keep increasing the speed. This is commonly referred to as the "power wall". Manufacturers of processors have instead begun to focus on building multi-core processors consisting of several cores working in parallel. Adapting program code to multi-core architectures constitutes a major challenge for software developers.Traditional simulation software uses centralized equation-system solvers, which by nature are hard to make parallel. By instead using distributed solvers, equations from different parts of the model can be solved simultaneously. For this to be effective, it is important to minimize overheadcosts and to make sure that the workload is evenly distributed over the processor cores.Dividing an equation system into several parts and solving them separately means that time delays will be introduced between the parts. If these occur in the right locations, this can be physically correct, since it also takes some time for information to propagate in physical systems. The transmission line element method (TLM) constitutes an effective method for separating system models by introducing impedances between components, causing physically motivated time delays.Contributions in this thesis include parts of the development of the new generation of the Hopsan simulation tool, with support for TLM and distributed solvers. An automatic algorithm for partitioning models has been developed. A multi-threaded simulation algorithm using barrier synchronization has also been implemented.Measurements of simulation time confirm that the simulation time is decreased almost proportionally to the number of processor cores for large models. The decrease, however, is reduced if the cores are divided on different processors. This was expected, due to the communication delay for processors communicating over shared memory. Experiments on real-time systems with four cores show that a four times as large model can be simulated without losing real-time performance.The division into distributed solvers constitutes a sort of natural cosimulation. A future project could be to use this as a platform for linking different simulation tools together and simulating them with high performance. This would make it possible to model each part of the system in the most suitable tool, and then connect all parts into one large model.
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| 6. |
- Dell’Amico, Alessandro
(författare)
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Pressure Control in Hydraulic Power Steering Systems
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a clear trend in the vehicle industry to implement more safetyrelated functions, where the focus is on active safety systems and today the steering system is also involved. Steering-related active safety functions can only be realised with a steering system that allows electroniccontrol of either the road wheel angle or the torque required to steer the vehicle, called active steering. The high power requirement of heavy vehicles means they must rely on hydraulic power to assist the driver. Thesystem is a pure hydro-mechanical system with an open-centre circuit activated by the driver’s steering action and suffers from poor energy efficiency. The main task of the hydraulic system is to control the pressure in the assistance cylinder in such a way that it eases the load on the driver.This work suggests a way to design and evaluate a self-regulating pressure control valve for use as actuator in the steering system. This valve can be made small and fast and is electronically controlled to enable active steering. It is based on a closed-centre circuit and has therefore the potential to improve energy efficiency. The aim of this work has been to investigate the possibility for the valve to perform as the original open-centre valve. The suggested approach is a model-based design and evaluation process where an optimisation routine is used to design the valve. Together with a validated model of the steering system, the new concept is compared with the original system. A hardware-inthe-loop simulation test rig has also been designed and built with the possibility to test a closed-centre steering system. It has partly been used to support the modelling process and partly to verify that a closedcentre steering system is a feasible solution. The simulation results have shown that the designed valve can perform sufficiently well compared to the original system.
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| 7. |
- Gerdes, Mike
(författare)
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Predictive Health Monitoring for Aircraft Systems using Decision Trees
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unscheduled aircraft maintenance causes a lot problems and costs for aircraft operators. This is due to the fact that aircraft cause significant costs if flights have to be delayed or canceled and because spares are not always available at any place and sometimes have to be shipped across the world. Reducing the number of unscheduled maintenance is thus a great costs factor for aircraft operators. This thesis describes three methods for aircraft health monitoring and prediction; one method for system monitoring, one method for forecasting of time series and one method that combines the two other methods for one complete monitoring and prediction process. Together the three methods allow the forecasting of possible failures. The two base methods use decision trees for decision making in the processes and genetic optimization to improve the performance of the decision trees and to reduce the need for human interaction. Decision trees have the advantage that the generated code can be fast and easily processed, they can be altered by human experts without much work and they are readable by humans. The human readability and modification of the results is especially important to include special knowledge and to remove errors, which the automated code generation produced.
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| 8. |
- Hallberg, Peter
(författare)
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Low-Cost Demonstrators : Enhancing Product Development with the Use of Physical Representations
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ever since the early nineties and the advent of affordable and comprehensive 3D-CAD systems, companies have striven to take advantage of cost-effective Virtual Prototyping, gradually moving away from activities involving physical representations of the evolving product. There are, however, aspects of the product development process that are less suitable for virtual exploration. Thus, there are limits to what extent it is effective to rely on digital modeling of physical products. Instead, this thesis argues that a deliberate combination of physical and virtual modeling offers numerous efficiencies that deserve further investigation.By studying and combining four domains; product development theory, traditional prototyping, computer aided engineering and learning theory, the concept of low-cost demonstrators are identified as a potential means for further enhancement of the product development process. Especially when developing products involving new and unfamiliar technologies, this approach has proven particularly relevant and beneficial. Furthermore, a low-cost demonstrator can potentially serve as a catalyst for innovation and creativity among the members of the design team operating in a CAE intense environment.In order to verify the validity of the concept of low-cost demonstrators, several undergraduate courses at Linköping University have been studied and evaluated.
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| 9. |
- Lundström, David
(författare)
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Aircraft Design Automation and Subscale Testing : With Special Reference to Micro Air Vehicles
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation concerns how design automation as well as rapid prototyping and testing of subscale prototypes can support aircraft design. A framework for design automation has been developed and is applied specifically to Micro Air Vehicles (MAV). MAVs are an interesting area for design automation as they are an application where the entire design, from requirements to manufacturing, can indeed be automated. From a complexity point of view it can be considered to be similar to conceptual design of manned aircraft.The created design optimization framework interfaces several software systems to generate MAVs to optimally fulfil specific mission requirements. The goal has been to find a method for MAV design and optimization from a holistic viewpoint, i.e. not a method for optimizing single subsystems, such as motor or propeller, but a method that embraces all disciplines of MAV design. Key drivers have been the use of off-the-shelf components wherever possible and to optimize the geometric shape not just from an aerodynamic perspective, but also to consider internal component placement and stability criteria. The optimization technique chosen is a multi-objective genetic algorithm. Finally, a novel method for direct digital manufacturing of MAVs is proposed.The utility of the framework has been demonstrated with several case studies on MAV design. The propulsion system is identified as most influential on MAV performance and thus is where it is most important to have accurate models. For this reason the models used in the framework are experimentally validated. The influence of atmospheric winds and turbulence on MAV performance is also experimentally investigatedThe subscale testing efforts are aimed at reducing cost and increasing the usability of flight testing with subscale vehicles. Data acquisition system design is described and low-cost testing methods are presented, such as car top testing or in-flight flow visualization. Two subscale flight projects are also presented.
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| 10. |
- Munjulury, Venkata Raghu Chaitanya
(författare)
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Knowledge Based Integrated Multidisciplinary Aircraft Conceptual Design
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the ever growing complexity of aircrafts, new tools and eventually methods to use these tools are needed in aircraft conceptual design. To reduce the development cost, an enhancement in the conceptual design is needed.This thesis presents a knowledge-based aircraft geometry design tool RAPID and the methodology applied in realizing the design. The parameters used to create a geometry need to be exchange between different tools. This is achieved by using a centralized database or onedata concept. One-database will enable creating a less number of cross connections between different tools to exchange data with one another. Different types of aircraft configurations can be obtained with less effort. As RAPID is developed based on relational design, any changes made to the geometric model will update automatically. The geometry model is carefully defined to carry over to the preliminary design.The validation of RAPID is done by implementing it in different aircraft design courses at Linköping University. In the aircraft project course, RAPID was effectively used and new features were added to the obtained desired design. Knowledge-base is used to realize the design performance for the geometry with an integrated database approach for a multidisciplinary aircraft conceptual design.
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