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  • Presentation: 2018-12-14 10:15 ACAS, A-huset, Linköping
    Wärner, Hugo
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    High-Temperature Fatigue Behaviour of Austenitic Stainless Steel: Influence of Ageing on Thermomechanical Fatigue and Creep-Fatigue Interaction2018Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The global energy consumption is increasing and together with global warming from greenhouse gas emission, create the need for more environmental friendly energy production processes. Higher efficiency of biomass power plants can be achieved by increasing temperature and pressure in the boiler section and this would increase the generation of electricity along with the reduction in emission of greenhouse gases e.g. CO2. The power generation must also be flexible to be able to follow the demands of the energy market, this results in a need for cyclic operating conditions with alternating output and multiple start-ups and shut-downs.

    Because of the demands of flexibility, higher temperature and higher pressure in the boiler section of future biomass power plants, the demands on improved mechanical properties of the materials of these components are also increased. Properties like creep strength, thermomechanical fatigue resistance and high temperature corrosion resistance are critical for materials used in the next generation biomass power plants. Austenitic stainless steels are known to possess such good high temperature properties and are relatively cheap compared to the nickel-base alloys, which are already operating at high temperature cyclic conditions in other applications. The behaviour of austenitic stainless steels during these widened operating conditions are not yet fully understood.

    The aim of this licentiate thesis is to increase the knowledge of the mechanical behaviour at high temperature cyclic conditions for austenitic stainless steels. This is done by the use of thermomechanical fatigue- and creepfatigue testing at elevated temperatures. For safety reasons, the effect of prolonged service degradation is investigated by pre-ageing before mechanical testing. Microscopy is used to investigate the microstructural development and resulting damage behaviour of the austenitic stainless steels after testing. The results show that creep-fatigue interaction damage, creep damage and oxidation assisted cracking are present at high temperature cyclic conditions. In addition, simulated service degradation resulted in a detrimental embrittling effect due to the deterioration by the microstructural evolution.

    1. Creep-Fatigue Interaction in Heat Resistant Austenitic Alloys
    Åpne denne publikasjonen i ny fane eller vindu >>Creep-Fatigue Interaction in Heat Resistant Austenitic Alloys
    2018 (engelsk)Inngår i: MATEC Web of Conferences 165 , 05001 (2018) / [ed] EDP Sciences, EDP Sciences, 2018, Vol. 165Konferansepaper, Publicerat paper (Fagfellevurdert)
    sted, utgiver, år, opplag, sider
    EDP Sciences, 2018
    HSV kategori
    urn:nbn:se:liu:diva-148182 (URN)10.1051/matecconf/2018165505001 (DOI)
    Fatigue 2018 , 12th International Fatigue Congress, 27 May-1 June 2018, Poitiers, France
    Tilgjengelig fra: 2018-06-01 Laget: 2018-06-01 Sist oppdatert: 2018-11-27
  • Presentation: 2018-12-18 10:15 Ada Lovelace, B-huset, Linköping
    Albrektsson, Jörgen
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Optimisation of Off-Road Transport Missions2018Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Mines, construction sites, road construction and quarries are examples of applications where construction equipment are used. In a production chain consisting of several construction machines working together, the work needs to be optimised and coordinated to achieve an environmental friendly, energy efficient and productive production. Recent rapid development within positioning services, telematics and human machine interfaces (HMI) opens up for control of individual machines and optimisation of transport missions where several construction machines co-operate.

    The production chain on a work site can be split up in different sub-tasks of which some can be transport missions. Taking off in a transport mission where one wheel loader ("loader" hereinafter) and two articulated haulers ("haulers" hereinafter) co-operate to transport material at a set production rate [ton/h], a method for fuel optimal control is developed. On the mission level, optimal cycle times for individual sub-tasks such as wheel loader loading, hauler transport and hauler return, are established through the usage of Pareto fronts.

    The haulers Pareto fronts are built through the development of a Dynamic Programming (DP) algorithm that trades fuel consumption versus cycle time for a road stretch by means of a time penalty constant. Through varying the time penalty constant n number of times, discrete fuel consumption - cycle time values can be achieved, forming the Pareto front. At a later stage, the same DP algorithm is used to generate fuel optimal vehicle speed and gear trajectories that are used as control signals for the haulers. Input to the DP algorithm is the distance to be travelled, road inclination, rolling resistance coefficient and a max speed limit to avoid unrealistic optimisation results.

    Thus, a method to describe the road and detect the road related data is needed to enable the optimisation. A map module is built utilising an extended Kalman Filter, Rauch-Tung-Striebel smoother and sensor fusion to merge data and estimate parameters not observable by sensors. The map module uses a model of the vehicle, sensor signals from a GPS or GNSS sensor and machine sensors to establish a map of the road.

    The wheel loader Pareto front is based on data developed in previous research combined with Volvo in-house data. The developed optimisation algorithms are implemented on a PC and in an interactive computer tablet based system. A human machine interface is created for the tablet, guiding the operators to follow the optimal control signals, which is speed for the haulers and cycle time for the loader. To evaluate the performance of the system it is tested in real working conditions.

    The contributions develop algorithms, set up a demo mission control system and carry out experiments. Altogether rendering in a platform that can be used as a base for a future design of an off-road transport mission control system.

    1. Road estimation and fuel optimal control of an off-road vehicle
    Åpne denne publikasjonen i ny fane eller vindu >>Road estimation and fuel optimal control of an off-road vehicle
    2017 (engelsk)Inngår i: Proceedings of the 3rd International Conference on Vehicle Technology and Intelligent Transport Systems, SciTePress, 2017, s. 58-67Konferansepaper, Publicerat paper (Fagfellevurdert)
    sted, utgiver, år, opplag, sider
    SciTePress, 2017
    HSV kategori
    urn:nbn:se:liu:diva-142731 (URN)10.5220/0006247200580067 (DOI)978-989-758-242-4 (ISBN)
    3rd International Conference on Vehicle Technology and Intelligent Transport Systems, VEHITS 2017, April 22-24, 2017, in Porto, Portugal
    Tilgjengelig fra: 2018-04-03 Laget: 2018-04-03 Sist oppdatert: 2018-11-22
    2. Fuel optimal control of an off-road transport mission
    Åpne denne publikasjonen i ny fane eller vindu >>Fuel optimal control of an off-road transport mission
    2018 (engelsk)Inngår i: 2018 IEEE International Conference on Industrial Technology (ICIT), 2018, s. 175-180Konferansepaper, Publicerat paper (Fagfellevurdert)
    HSV kategori
    urn:nbn:se:liu:diva-151856 (URN)10.1109/ICIT.2018.8352172 (DOI)978-1-5090-5949-2 (ISBN)
    2018 IEEE International Conference on Industrial Technology (ICIT), 19-22 Feb.,Lyon, France
    Tilgjengelig fra: 2018-10-06 Laget: 2018-10-06 Sist oppdatert: 2018-11-22
  • Presentation: 2018-12-19 10:15 Alan Turing, E-huset, Linköping
    Falkenjack, Johan
    Linköpings universitet, Institutionen för datavetenskap, Interaktiva och kognitiva system. Linköpings universitet, Tekniska fakulteten.
    Towards a Model of General Text Complexity for Swedish2018Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    In an increasingly networked world, where the amount of written information is growing at a rate never before seen, the ability to read and absorb written information is of utmost importance for anything but a superficial understanding of life's complexities. That is an example of a sentence which is not very easy to read. It can be said to have a relatively high degree of text complexity. Nevertheless, the sentence is also true. It is important to be able to read and understand written materials. While not everyone might have a job where they have to read a lot, access to written material is necessary in order to participate in modern society. Most information, from news reporting, to medical information, to governmental information, come primarily in a written form.

    But what makes the sentence at the start of this abstract so complex? We can probably all agree that the length is part of it. But then what? Researches in the field of readability and text complexity analysis have been studying this question for almost 100 years. That research has over time come to include many computational and data driven methods within the field of computational linguistics.

    This thesis cover some of my contributions to this field of research, though with a main focus on Swedish rather than English text. It aims to explore two primary questions (1) Which linguistic features are most important when assessing text complexity in Swedish? and (2) How can we deal with the problem of data sparsity with regards to complexity annotated texts in Swedish?

    The first issue is tackled by exploring the task of identifying easy-to-read ("lättläst") text using classification with Support Vector Machines. A large set of linguistic features is evaluated with regards to predictive performance and is shown to separate easy-to-read texts from regular texts with a very high accuracy. Meanwhile, using a genetic algorithm for variable selection, we find that almost the same accuracy can be reached with only 8 features. This implies that this classification problem is not very hard and that results might not generalize to comparing less easy-to-read texts.

    This, in turn, brings us to the second question. Except for easy-to-read labeled texts, the data with text complexity annotations is very sparse. It consist of multiple small corpora using different scales to label documents. To deal with this problem, we propose a novel statistical model. The model belongs to the larger family of Probit models and is implemented in a Bayesian fashion and estimated using a Gibbs sampler based on extending a well established Gibbs sampler for the Ordered Probit model. This model is evaluated using both simulated and real world readability data with very promising results.