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  • 122101. Yeung, E.
    et al.
    Goncalves, J.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Warnick, S.
    Mathematical relationships between representations of structure in linear interconnected dynamical systems2011In: 2011 AMERICAN CONTROL CONFERENCE, 2011, p. 4348-4353Conference paper (Refereed)
    Abstract [en]

    A dynamical system can exhibit structure on multiple levels. Different system representations can capture different elements of a dynamical system’s structure. We consider LTI input-output dynamical systems and present four representations of structure: complete computational structure, subsystem structure, signal structure, and input output sparsity structure. We then explore some of the mathematical relation ships that relate these different representations of structure. In particular, we show that signal and subsystem structure are fundamentally different ways of representing system structure. A signal structure does not always specify a unique subsystem structure nor does subsystem structure always specify a unique signal structure. We illustrate these concepts with a numerical example.

  • 122102. Yeung, E.
    et al.
    Goncalves, J.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Warnick, S.
    Network structure preserving model reduction with weak a priori structural information2009In: 48th IEEE Conference on Decision and Control held jointly with 2009 28th Chinese Control Conference, CDC/CCC 2009, 2009, p. 3256-3263Conference paper (Refereed)
    Abstract [en]

    This paper extends a state projection method for structure preserving model reduction to situations where only a weaker notion of system structure is available. This weaker notion of structure, identifying the causal relationship between manifest variables of the system, is especially relevant is settings such as systems biology, where a clear partition of state variables into distinct subsystems may be unknown, or not even exist. The resulting technique, like similar approaches, does not provide theoretical performance guarantees, so an extensive computational study is conducted, and it is observed to work fairly well in practice. Moreover, conditions characterizing structurally minimal realizations and sufficient conditions characterizing edge loss resulting from the reduction process, are presented.

  • 122103. Yeung, E.
    et al.
    Goncalves, J.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Warnick, S.
    Representing structure in linear interconnected dynamical systems2010In: 49TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC), 2010, p. 6010-6015Conference paper (Refereed)
    Abstract [en]

    Interconnected dynamical systems are a pervasive component in our modern world’s infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is determining how to appropriately represent their structure. In this work, we discuss different ways of representing a system’s structure. We define and present, in particular, four representations of system structure-complete computational, subsystem, signal, and zero pattern structure-and discuss some of their fundamental properties. We illustrate their application with a numerical example and show how radically different representations of structure can be consistent with a single LTI input-output system.

  • 122104. Yeung, Millan K.
    et al.
    Gui, Z.
    Wong, B.
    Orban, P.
    Wang, Lihui
    Integrated Manufacturing Technologies Institute, National Research Council Canada.
    Lang, Sherman Y. T.
    High Performance Machining Automation2005In: Proceedings of the 5th International Workshop on Advanced Manufacturing Technologies, 2005, p. 225-230Conference paper (Refereed)
  • 122105. Yeung, Millan K.
    et al.
    Wang, Lihui
    Orban, Peter
    Development of Machining Topology Knowledge Base2003Conference paper (Refereed)
  • 122106.
    Yevseyeva, Iryna
    et al.
    Department of Mathematical Information Technology, University of Jyväskylä, Finland.
    Miettinen, Kaisa
    Helsinki School of Economics.
    Survey of Multicriteria Decision Aiding Methods for Ordinal Classification with Some New Methodology2005Report (Other academic)
  • 122107.
    Yevseyeva, Iryna
    et al.
    Department of Mathematical Information Technology, University of Jyväskylä, Finland.
    Miettinen, Kaisa
    Helsinki School of Economics.
    Räsänen, P.
    Decision Support System for Attention Deficit Hyperactivity Disorder Diagnostics2005In: Proceedings of ORP3, Operational Research Peripatetic Postgraduate Programme / [ed] C. Maroto, R. Ruiz, J. Alcaraz, E. Vallada, F. Crespo, 2005, p. 183-194Conference paper (Refereed)
  • 122108.
    Yevseyeva, Iryna
    et al.
    Department of Mathematical Information Technology, University of Jyväskylä, Finland.
    Miettinen, Kaisa
    Helsinki School of Economics.
    Salminen, Pekka
    School of Business and Economics, University of Jyväskylä.
    Lahdelma, Risto
    Department of Information Technology, University of Turku.
    SMAA-Classification - A New Method for Nominal Classification2007Report (Other academic)
    Abstract [en]

    We have developed a multicriteria decision aiding method for nominal classification for situations where prefer-ence information is imprecise, uncertain or absent. Such situations may appear, for instance, when the decisionmaker is not sure about his or her preferences or when there are multiple decision makers who have difficulties inagreeing about their common preference. The new SMAA-Classification method extends Stochastic Multicrite-ria Acceptability Analysis (SMAA) methodology for classification problems. The method provides the decisionmaker with descriptive information in the form of acceptability index for each alternative to be classified intoeach predefined class. We test the new method with several applications.

  • 122109.
    Yezeguelian, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Flight Dynamics.
    Modelling and Simulation of a Propulsive Hybridisation for a Light Fixed-wing Aircraft2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Propulsive hybridisation fits in with the sustainable development policies of many companies which are part of the transportation industry. Actually, it makes it possible either to reduce fuel consumption or to improve the aircraft performance at a fixed fuel burn. However, the current technologies of batteries restrain a more regular use in light aviation. For this project this issue is confirmed as both the quasi-static performance assessment and the dynamic studies show that the endurance objective cannot be improved with Li/Ion batteries. However, it is possible to act directly on the engine performance by placing a thermal energy recovery system on exhaust gas pipes to take advantage of their high temperatures, greatly boosting the aircraft performance in cruise.

  • 122110.
    Yi, He
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Agent-based Material Planning for Evolvable Production System2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The two main characteristics of current market are dynamicity and unpredictability which can’t be satisfied by the traditional manufacturing system through pre-set parameters. Traditional production system is facing the challenge that evolves to a new generation manufacturing system which manufactures products in flexible volume with rapid product definition and system configuration. The advent of Evolvable Production System offers promising approach to adapt to the increasing customer consciousness and product differentiation. EPS improves system re-configurability by process-oriented modularity and multi-agent based distributed control system.

    Hakan Akillioglu (2011) proposed a demand responsive planning framework to enlighten the relation between planning system structure and the manufacturing system characteristics. The proposed planning is still at the preliminary phase, it contains the coherent flow of planning activities and aims to achieve complementary model of production system and planning framework.

    This thesis is based on Hakan’s planning framework and focus on the development of the domain between material inventory and the material on the shop floor. The critical prerequisite of the proposed model is that material required to be delivered in the right type material, right amount and at the right location and right time under the dynamic environment of EPS.

  • 122111.
    Yi, Pan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    The planning for biofuels: China's dilemma.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A current discussion of winner and loser is the issue of low-carbon development toward sustainability. Biofuel, as granted an important role to curtail the carbon emission and secure energy supply, has been also involved in this discussion. However, unfortunately, a biofuel potential has been raising fear worldwide since the surge of its development favors large-scale patterns, which are bringing widely social-economical and environmental impacts. How to foster strengths and circumvent weaknesses to plan this sector is the core of this paper. China has emerged to be the second economic entity with huge appetite for energy. This study is expected to explain China’s experiences in this field with guidance of effective biofuel planning.

  • 122112.
    Yi, Xiaokun
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Adaptive Wireless Multimedia Services2006Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Context-awareness is a hot topic in mobile computing currently. A lot of importance is being attached to facilitating the user of various mobile computing devices to provide services that are more “user-centric”. One aspect of context-awareness is to perceive variations in available resources, and to make decisions based on the feedback to enable applications to automatically adapt to the current environment.

    For Voice over IP (VoIP) software phones (softphones), variations in network performance lead to fluctuations in the quality of the communication. Therefore, by making these softphones more adaptive to the network environment will, to some extent, mask such fluctuations. Dynamic voice and video adaptation derives from the fact that different coder-decoders (CODEC) have different characteristics, even the same CODECs with a different configuration can behave quite differently, in terms of bandwidth consumption, packet size, etc.

    Minisip is a VoIP client application which was implemented on and targeted for a Linux platform. One of my tasks was to port Minisip to Microsoft’s Windows Mobile operating system, running on an HP IPAQ Pocket PC H5550. Such handheld computer enables the user to communication while they are moving about, thus increasing the probability that the characteristics of the network connection will change. Building upon this port, the next task was to add dynamic voice and video CODEC adaptation. Dynamic voice and video CODEC adaptation on Minisip poses several challenges, for example, in what way can the network performance be determined and what adaptation strategy can achieve high call quality while making efficient utilization of available network resources.

    In order to make the proper design choices, several estimation models will be discussed, these are used to determine an efficient, un-intrusive, and light weight means of dynamic CODEC selection within Minisip. This thesis only implemented audio CODEC adaptation of Minisip, and the evaluation of the resulting prototype shows that such dynamic adaptation is both feasible and practical; further more, video CODEC adaptation would be a more significant extension to this work in the future.

  • 122113.
    Yi, Xinlei
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Resource-Constrained Multi-Agent Control Systems: Dynamic Event-triggering, Input Saturation, and Connectivity Preservation2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    978-91-7729-579-2A multi-agent system consists of multiple agents cooperating to achieve a common objective through local interactions. An important problem is how to reduce the amount of information exchanged, since agents in practice only have limited energy and communication resources. In this thesis, we propose dynamic event-triggered control strategies to solve consensus and formation problems for multi-agent systems under such resource constraints.

    In the first part, we propose dynamic event-triggered control strategies to solve the average consensus problem for first-order continuous-time multi-agent systems. It is proven that the state of each agent converges exponentially to the average of all agents' initial states under the proposed triggering laws if and only if the underlying undirected graph is connected.In the second part, we study the consensus problem with input saturation over directed graphs. It is shown that the underlying directed graph having a directed spanning tree is a necessary and sufficient condition for achieving consensus. Moreover, in order to reduce the overall need of communication and system updates, we propose an event-triggered control strategy to solve this problem. It is shown that consensus is achieved, again, if and only if the underlying directed graph has a directed spanning tree.In the third part, dynamic event-triggered formation control with connectivity preservation is investigated. Single and double integrator dynamics are considered. All agents are shown to converge to the formation exponentially with connectivity preservation.The effectiveness of the theoretical results in the thesis is verified by several numerical examples.

  • 122114.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Liu, Kun
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Dynamic Event-Triggered Control for Multi-Agent Systems2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE, 2017, p. 6683-6688Conference paper (Refereed)
    Abstract [en]

    We propose two distributed dynamic triggering laws to solve the consensus problem for multi-agent systems with event-triggered control. Compared with existing triggering laws, the proposed triggering laws involve internal dynamic variables which play an essential role to guarantee that the triggering time sequence does not exhibit Zeno behavior. Some existing triggering laws are special cases of our dynamic triggering laws. Under the condition that the underlying graph is undirected and connected, it is proven that the proposed dynamic triggering laws together with the event-triggered control make the state of each agent converges exponentially to the average of the agents’ initial states. Numerical simulations illustrate the effectiveness of the theoretical results and show that the dynamic triggering laws lead to reduction of actuation updates and inter-agent communications.

  • 122115.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Liu, Kun
    Beijing Inst Technol, Sch Automat, Beijing 100081, Peoples R China..
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Dynamic Event-Triggered and Self-Triggered Control for Multi-agent Systems2019In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 64, no 8, p. 3300-3307Article in journal (Refereed)
    Abstract [en]

    We propose two novel dynamic event-triggered control laws to solve the average consensus problem for first-order continuous-time multiagent systems over undirected graphs. Compared with the most existing triggering laws, the proposed laws involve internal dynamic variables, which play an essential role in guaranteeing that the triggering time sequence does not exhibit Zeno behavior. Moreover, some existing triggering laws are special cases of ours. For the proposed self-triggered algorithm, continuous agent listening is avoided as each agent predicts its next triggering time and broadcasts it to its neighbors at the current triggering time. Thus, each agent only needs to sense and broadcast at its triggering times, and to listen to and receive incoming information from its neighbors at their triggering times. It is proved that the proposed triggering laws make the state of each agent converge exponentially to the average of the agents' initial states if and only if the underlying graph is connected. Numerical simulations are provided to illustrate the effectiveness of the theoretical results.

  • 122116.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Liu, Kun
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Dynamic Triggering Laws and Predictive Self-Triggered Algorithm for Multi-Agent Systems with Event-triggered ControlManuscript (preprint) (Other academic)
    Abstract [en]

    We propose two distributed dynamic triggering laws and one predictive self-triggered algorithm to solve the consensus problem for multi-agent systems with event-triggered control. Compared with existing triggering laws, the proposed triggering laws involve internal dynamic variables which play an essential role to guarantee that the triggering time sequence does not exhibit Zeno behavior. Some existing triggering laws are special cases of our dynamic triggering laws. Unlike the great majority of existing works that propose distributed triggering laws and self-triggered algorithm, continuous listening is avoided in the proposed predictive self-triggered algorithm.

    Under the condition that the underlying graph is undirected and connected, it is proven that the proposed dynamic triggering laws and the predictive self-triggered algorithm together with the event-triggered control make the state of each agent converges exponentially to the average of the agents’ initial states. Numerical simulations illustrate the effectiveness of the theoretical results and show that the dynamic triggering laws and the predictive self-triggered algorithm lead to reduction of actuation updates and inter-agent communications.

  • 122117.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Fudan Univ, Sch Math Sci, Shanghai 200433, Peoples R China..
    Lu, Wenlian
    Fudan Univ, Sch Math Sci, Shanghai 200433, Peoples R China.;Fudan Univ, Ctr Computat Syst Biol, Shanghai 200433, Peoples R China..
    Chen, Tianping
    Fudan Univ, Sch Math Sci, Shanghai 200433, Peoples R China.;Fudan Univ, Sch Comp Sci, Shanghai 200433, Peoples R China..
    Centralized Event-triggered Control for Linear Multi-agent Systems2016In: PROCEEDINGS OF THE 28TH CHINESE CONTROL AND DECISION CONFERENCE (2016 CCDC), IEEE , 2016, p. 225-230Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the consensus problem of linear multi-agent systems. Centralized event-triggered rules are provided so as to reduce the frequency of system's updating. The diffusion coupling feedbacks of each agent are based on the latest observations from its in-neighbours and the system's next observation time is triggered by a criterion based on all agents' information. The scenario of continuous monitoring is first considered, namely all agents' instantaneous states can be observed. It is proved that if the network topology is connected, then this centralized event-triggered coupling strategy can realize consensus exponentially for the linear multi-agent systems. Then the results are extended to discontinuous monitoring, where the system computes its next triggering time in advance without having to observe all agents' states continuously. As a special case, we apply above results to double-integrator consensus problem. One example with numerical simulation are provided to show the effectiveness of the theoretical results.

  • 122118.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wei, Jieqiang
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Formation Control for Multi-Agent Systems with Connectivity Preservation and Event-Triggered Controllers2017In: IFAC-PapersOnLine, ISSN 1045-0823, E-ISSN 1797-318X, Vol. 50, no 1, p. 9367-9373Article in journal (Refereed)
    Abstract [en]

    In this paper, event-triggered controllers and corresponding algorithms are proposed to establish the formation with connectivity preservation for multi-agent systems. Each agent needs to update its control input and to broadcast this control input together with the relative state information to its neighbors at its own triggering times, and to receive information at its neighbors' triggering times. Two types of system dynamics, single integrators and double integrators, are considered. As a result, all agents converge to the formation exponentially with connectivity preservation, and Zeno behavior can be excluded. Numerical simulations show the effectiveness of the theoretical results.

  • 122119.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wei, Jieqiang
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Formation Control for Multi-Agent Systems with Connectivity Preservation and Predictive Self-Triggered ControllersManuscript (preprint) (Other academic)
    Abstract [en]

    In this paper, event-triggered algorithms and predictive self-triggered algorithms are proposed to establish the formation with connectivity preservation for multi-agent  ystems.

    Each agent only needs to update its control input by sensing the relative state information and to broadcast its triggering information to its neighbors at its own triggering times, and to listen and to receive its neighbors' triggering information at their triggering times. Two types of system dynamics, single integrators and double integrators, are considered. As a result, all agents converge to the formation exponentially with connectivity preservation and exclusion of Zeno behavior. Numerical simulations show the eectiveness of the theoretical results.

  • 122120.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wei, Jieqiang
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Self-Triggered Control for Multi-Agent Systems with Quantized Communication or Sensing2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 2227-2232, article id 7798594Conference paper (Refereed)
    Abstract [en]

    The consensus problem for multi-agent systems with quantized communication or sensing is considered. Centralized and distributed self-triggered rules are proposed to reduce the overall need of communication and system updates. It is proved that these self-triggered rules realize consensus exponentially if the network topologies have a spanning tree and the quantization function is uniform. Numerical simulations are provided to show the effectiveness of the theoretical results.

  • 122121.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yang, Tao
    Wu, Junfeng
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control.
    Distributed Event-Triggered Control for Global Consensus of Multi-Agent Systems with Input SaturationManuscript (preprint) (Other academic)
    Abstract [en]

    We consider the global consensus problem for multi-agent systems with input saturation over digraphs. Under a mild connectivity condition that the underlying digraph has a directed spanning tree, we use Lyapunov methods to show that the widely used distributed consensus protocol, which solves the consensus problem for the case without input saturation constraints, also solves the global consensus problem for the case with input saturation constraints. In order to reduce the overall need of communication and system updates, we then propose a distributed event-triggered control law. Global consensus is still realized and Zeno behavior is excluded. Numerical simulations are provided to illustrate the effectiveness of the theoretical results.

  • 122122.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Yang, Tao
    Univ North Texas, Dept Elect Engn, Denton, TX 76203 USA..
    Wu, Junfeng
    Zhejiang Univ, Coll Control Sci & Engn, Hangzhou 310027, Zhejiang, Peoples R China..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Distributed event-triggered control for global consensus of multi-agent systems with input saturation2019In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 100, p. 1-9Article in journal (Refereed)
    Abstract [en]

    The global consensus problem for first-order continuous-time multi-agent systems with input saturation is considered. In order to reduce the overall need of communication and system updates, we propose an event-triggered consensus protocol and a triggering law, which do not require any a priori knowledge of global network parameters. It is shown that Zeno behavior is excluded for these systems and that the underlying directed graph having a directed spanning tree is a necessary and sufficient condition for global consensus. We use a new Lyapunov function to show the sufficient condition and it inspires the triggering law. Numerical simulations are provided to illustrate the effectiveness of the theoretical results.

  • 122123.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yang, Tao
    Wu, Junfeng
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Event-Triggered Control for Multi-Agent Systems with Output Saturation2017In: 2017 36th Chinese Control Conference (CCC), IEEE Computer Society, 2017, p. 8431-8436, article id 8028693Conference paper (Refereed)
    Abstract [en]

    We propose distributed static and dynamic event-triggered control laws to solve the consensus problem for multiagent systems with output saturation. Under the condition that the underlying graph is undirected and connected, we show that consensus is achieved under both event-triggered control laws if and only if the average of the initial states is within the saturation level. Numerical simulations are provided to illustrate the effectiveness of the theoretical results and to show that the control laws lead to reduced need for inter-agent communications.

  • 122124.
    Yi, Xinlei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Yao, Lisha
    Univ North Texas, Dept Elect Engn, Denton, TX 76203 USA..
    Yang, Tao
    Univ North Texas, Dept Elect Engn, Denton, TX 76203 USA..
    George, Jemin
    US Army Res Lab, Adelphi, MD 20783 USA..
    Johansson, Karl H.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Distributed Optimization for Second-Order Multi-Agent Systems with Dynamic Event-Triggered Communication2018In: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, p. 3397-3402Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a fully distributed algorithm for second-order continuous-time multi-agent systems to solve the distributed optimization problem. The global objective function is a sum of private cost functions associated with the individual agents and the interaction between agents is described by a weighted undirected graph. We show the exponential convergence of the proposed algorithm if the underlying graph is connected, each private cost function is locally gradient-Lipschitz- continuous, and the global objective function is restricted strongly convex with respect to the global minimizer. Moreover, to reduce the overall need of communication, we then propose a dynamic event-triggered communication mechanism that is free of Zeno behavior. It is shown that the exponential convergence is achieved if the private cost functions are also globally gradient-Lipschitz- continuous. Numerical simulations are provided to illustrate the effectiveness of the theoretical results.

  • 122125. Yi, Y.
    et al.
    Chen, Jiajia
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Service chain placement in server-centric optical datacenter networks2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)
    Abstract [en]

    We propose and compare several heuristics service chain (SC) placement algorithms tailored for the server-centric optical interconnect architecture, providing a guideline on how to efficiently place SCs in such an optical datacenter network.

  • 122126.
    Yideti, Tatek Fekadu
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Packing theory-based Framework for Performance Evaluation of Unbound Granular Materials2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Enhancing the load bearing quality of granular layers is fundamental to optimize the structural performance of the pavements. Unbound granular materials are one of the most used materials in the base layers of pavements. There have been growing interests on the behavior of unbound granular material in road base layers. Both design of a new pavement and prediction of service life need proper characterization of unbound granular materials, which is one of the requirements for a new mechanistic pavement design methods.

    Adequate knowledge of the strength and deformation characteristics of unbound layers in pavements is essential for proper thickness design, residual life determination, and economic optimization of the pavement structure. The current knowledge concerning granular materials employed in pavement structures is limited. In addition, to date, no general framework has been established to explain and evaluate satisfactorily the behavior of unbound granular materials under the complex repeated loading which they experience.

    This thesis presents a packing theory-based framework to evaluate the mechanical properties of unbound granular materials. The framework was developed based on the particle-to-particle contact, the particle size distribution and the packing arrangement. The skeleton of the unbound materials should be composed of both coarse enough particles and a limited amount of fine granular materials to effectively resist deformation and carry traffic loads. Based on this, the framework identifies the two basic components of unbound granular materials, namely the primary structure (PS) - a range of interactive coarse grain sizes that forms the main load carrying network in granular materials and the secondary structure (SS) - a range of grain sizes smaller than the PS providing stability to the aggregate skeleton.

    In the framework, disruption potential (DP), PS porosity, PS coordination number and void ratio of skeleton (PS+SS) are among the key packing parameters which were established from the framework. These parameters were validated by evaluating the permanent deformation, resilient modulus and California bearing ratio of unbound granular materials using different materials with various experimental results.

    Furthermore, in this thesis a new moisture distribution model (Birgisson-Jelagin-Yideti (BJY) moisture distribution model) was introduced. In the model, SS particles associated with water retention. The water is stored as meniscus water between these small particles and fully filled in small voids. The volume of meniscus water between SS particles and the measured matric suction values are the two key parameters considered in the model. The results showed that the model developed is capable of predicting the experimentally measured matric suction values for a range of gradations.

    Finally, the application of shakedown and packing theories to characterize permanent deformation behaviour of unbound aggregate materials is presented. A simple finite element analysis has also been simulated in order to find out the effect of disruption potential on the shakedown limit load. Experimental results were used for the simulation of the finite element and compared favourably with the predicted mean stress and dimensionless shakedown load using DP values.

  • 122127.
    Yideti, Tatek Fekadu
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Performance model for unbound grnular materials pavements2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Recently, there has been growing interest on the behaviour of unbound granular material in road base layers. Researchers have studied that the design of a new pavement and prediction of service life need proper characterization of unbound granular materials, which is one of the requirements for a new mechanistic design method in flexible pavement.

    Adequate knowledge of the strength and deformation characteristics of unbound layer in pavements is a prerequisite for proper thickness design, residual life determination, and overall economic optimization of the pavement structure. The current knowledge concerning the granular materials employed in pavement structures is limited. In addition, to date, no general framework has been established to explain satisfactorily the behaviour of unbound granular materials under the complex repeated loading which they experience.

    In this study, a conceptual method, packing theory-based model is introduced; this framework evaluates the stability and performance of granular materials based on their packing arrangement. In the framework two basic aggregate structures named as Primary Structure (PS), and Secondary Structure (SS). The Primary Structure (PS) is a range of interactive grain sizes that forms the network of unbound granular materials. The Secondary Structure (SS) includes granular materials smaller than the primary structure. The Secondary Structures fill the gaps between the particles in the Primary Structure and larger particles essentially float in the skeleton.

    In this particular packing theory-based model; the Primary Structure porosity, the average contact points (coordination number) of Primary Structure, and a new parameter named Disruption Potential are the key parameters that determine whether or not a particular gradation results in a suitable aggregate structure.

    Parameters mentioned above play major role in the aggregate skeleton to perform well in terms of resistance to permanent deformation as well as load carrying capacity (resilient modulus). The skeleton of the materials must be composed of both coarse enough and a limited amount of fine granular materials to effectively resist deformation and carry traffic loads.

  • 122128.
    Yideti, Tatek Fekadu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    A new moisture distribution model for unbound granular materialsIn: Geotechnique, ISSN 0016-8505, E-ISSN 1751-7656Article in journal (Other academic)
    Abstract [en]

    The presence of waterin the unbound granular materials significantly influences the mechanicalperformance of the material. The ability to estimate the soil watercharacteristic curve (SWCC) is crucial thus to determine the effect themoisture has on the mechanical behaviour of granular materials. In this paper,an analytical moisture distribution model is proposed. A packing theory-based framework to evaluateperformance of unbound granular materials reported previously by the authorsallows identifying the two basic components of the unbound granular materialsskeleton: primary structure (PS) - a range of interactive coarse grain sizes thatforms the main load carrying network in granular materials and secondarystructure (SS) - a range of grain sizes smaller than the PS providing stabilityto the aggregate skeleton. In the new moisture distribution model presented inthis paper, moisture wasconsidered to be stored as meniscus water between SS particles and water thatfilled in small voids.The volume of meniscus water between SS particles and the measured matricsuction values are the two key parameters in the model. In order to validatethe model predicted results are then compared with measuredmatric suction of granite granular materials with different gradations. Theresults showed that the model developed is capable of predicting theexperimentally measured matric suction values for a range of gradations. 

  • 122129.
    Yideti, Tatek Fekadu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Influence of aggregate packing structure on California bearing ratio values of unbound granular materials2014In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 15, no 1, p. 102-113Article in journal (Refereed)
    Abstract [en]

    Over the past several decades, California bearing ratio (CBR) value has been used in many countries for empirical pavement designs and still many countries are using it for unbound granular materials strength measurement and as input to their pavement design chart. Furthermore, CBR value of unbound granular material is frequently correlated with its fundamental mechanical properties such as resilient modulus, which in turn is often used as an input to a mechanistic pavement design procedure. In the present study, the effect the aggregate packing has on the CBR values of unbound materials is investigated. A packing theory-based framework that allows to identify the load-carrying part of the aggregate skeleton is presented. Aggregate packing parameters controlling the CBR performance of the unbound materials are introduced and evaluated with the experimentally measured CBR values of 20 unbound granular materials found in the literature. It is shown that the CBR values of granular materials are to a great extent controlled by the packing characteristics of their load-carrying skeleton.

  • 122130.
    Yideti, Tatek Fekadu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Packing theory-based framework for evaluating resilient modulus of unbound granular materials2014In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 15, no 8, p. 689-697Article in journal (Refereed)
    Abstract [en]

    Enhancing the quality of granular layers is fundamental to optimise the structural performance of the pavements. The objective of this study is to investigate whether previously developed packing theory-based aggregate parameters can evaluate the resilient modulus of unbound granular materials. In this study, 19 differently graded unbound granular materials from two countries (USA and Sweden) were evaluated. This study validated both porosity of primary structure (PS) and contact points per particle (coordination number) as key parameters for evaluating the resilient modulus of unbound granular materials. This study showed that decreasing the PS porosity - higher coordination number - calculated based on the proposed gradation model, yields higher resilient modulus. Good correlation was observed between the proposed packing parameters and resilient modulus of several types of aggregates. The packing theory-based framework successfully recognised granular materials that exhibited poor performance in terms of resilient modulus.

  • 122131.
    Yideti, Tatek Fekadu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Jelagin, Denis
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Guarin, Alvaro
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Packing theory-based framework to evaluate permanent deformation of unbound granular materials2013In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 14, no 3, p. 309-320Article in journal (Refereed)
    Abstract [en]

    Permanent deformation of unbound granular materials plays an essential role in the long-term performance of a pavement structure. Stability of unbound granular materials is defined by the particle-to-particle contact of the system, the particle size distribution and the packing arrangement. This paper presents a gradation model based on packing theory to evaluate permanent deformation of unbound granular materials. The framework was evaluated by using 10 unbound granular materials from different countries. The disruption potential, which determines the ability of secondary structure (SS) to disrupt the primary structure (PS), is introduced. This study also identified the amount of PS and SS that may eventually be used as a design parameter for permanent deformation of unbound road layers. The evaluation of the model regarding permanent deformation behaviour of granular materials is found to compare favourably with experimental results.

  • 122132.
    Yideti, Tatek Fekadu
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Dawson, Andrew
    The University of Nottingham.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Implementation of Shakedown and Packing theories for Unbound Granular materialsIn: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526Article in journal (Other academic)
    Abstract [en]

    The shakedown theory is a tool to characterize the state of the structural system of an unbound granular material that is subjected to repeated loading when its response has become resilient in nature and no further accumulation of plastic strain occurs. This paper demonstrates the application of both shakedown and packing theories to characterize permanent deformation behaviour of unbound aggregate materials. Ranges of shakedown phenomenon (Ranges A, B and C) for some selected unbound materials have first been investigated based on their permanent strain responses. The disruption potential (DP) of the primary structure (PS) of the aggregate assemblage has then been determined for each grain size distribution based on a packing theory model. The DP was found to characterize satisfactorily the three types of shakedown ranges. A sensitivity analysis has also been done on DP values by changing the dry density and specific gravity, revealing the importance of these characteristics for shakedown. Further, a finite element analysis was performed to determine the shakedown limit load as a mean stress and a dimensionless shakedown load. The analysis was simulated using the Mohr-coulomb yield criteria for a three-dimensional cylindrical sample. From this study the DP value was found to compare favorably with the predicted mean stress and dimensionless shakedown load.

     

  • 122133.
    Yideti, Tatek
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Jelagin, Denis
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Moisture Distribution Model to Predict Matric Suction in Unbound Granular Materials as a Function of Fines Content2016In: TRB 95th Annual Meeting Compendium of Papers, 2016Conference paper (Refereed)
    Abstract [en]

    The existence of water in the layers of unbound road aggregates significantly influences the performance of pavement structure. Thus, the ability to estimate volumetric water content and its capillary effect is very important. Several models have been suggested to link the matric suction of unbound materials to their water retention properties. In this paper, an analytical moisture distribution model is proposed by using packing theory-based framework for unbound granular materials. The framework was previously developed by the authors of this paper and identifies two basic components of unbound granular materials skeleton: primary structure (PS) - a range of interactive coarse grain sizes that forms the main load-carrying network in granular materials and secondary structure (SS) - a range of grain sizes smaller than the PS providing stability to the aggregate skeleton. In the new moisture model, water was considered to be stored as both menisci water between SS particles and water that fully filled in very small voids. In order to validate the model, predicted results are compared with measured matric suction of a granite material with different gradations. The results showed that the model is capable of predicting the experimentally measured matric suction values for a range of gradations.

  • 122134.
    Yifan, Zheng
    KTH, School of Engineering Sciences (SCI), Physics.
    Research on a material discrimination method by cosmic ray muon tomography2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 122135.
    Yifang, Ban
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatics.
    Gong, Peng
    Tsinghua University.
    Gini, Chandra
    Global land cover mapping using earth observation satellite data: recent progresses and challenges2015In: ISPRS journal of photogrammetry and remote sensing (Print), ISSN 0924-2716, E-ISSN 1872-8235, Vol. 103, no 1, p. 1-6Article in journal (Refereed)
  • 122136.
    Yika Tuesta, Alberto Stavros
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Dielectrophoresis (DEP) and electrowetting (EWOD) as Anti-fouling processes for antibacterial surfaces2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today the medical field is struggling to decrease bacteria biofilm formation which leads to infection. Also, biomedical devices sterilization has not changed over a long period of time which has resulted in high costs for hospitals healthcare managements. The objective of this project is to investigate electro-dynamic effects by surface energy manipulation as potential methods for preventing bacteria biofilm growing on medical devices.

    Based on electrokinetic environments two different methods were tested: rejection bacteria dielectrophoretic forces feasibility by numerical simulations; and electrowetting-on -dielectric by the fabrication of golden interdigitated electrodes on silicon glass substrates covered by a Teflon layer.

    In the first experiment, numerical simulations of gold electrodes in buffer solution and frequencies were carried out to determine the forces required to reject bacteria. In the second experiment, interdigitated gold electrodes coated with a dielectric Teflon layer, were characterized in terms of breakdown voltage, dielectric adhesion and contact angle in terms of applied voltage. Finally the effect of EWOD on bacterial adhesion was tested.

    The project resulted in promising simulation results for bacteria rejection using dielectrophoresis due to the wide range of frequency that rejects the modelled bacteria. However, practical experiments such as electrowetting-on-dielectric must verify this at incubation times larger than 24 hours in spite of the Teflon non-adhesive properties.

  • 122137. Yildirim, H. C.
    et al.
    Marquis, Gary
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Notch stress analyses of high-frequency mechanical impact-improved welds by using rho(f) = 1 mm and rho(f) = rho + 1 mm approaches2014In: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 37, no 5, p. 561-569Article in journal (Refereed)
    Abstract [en]

    This paper presents further assessments of the previously reported round-robin fatigue data obtained from high-frequency mechanical impact (HFMI)-improved longitudinal welds. A detailed statistical analyses of geometry measurements of HFMI-treated weld toe profiles are presented. The fatigue analyses based on notch stress as defined by the International Institute of Welding are performed using the finite element method. Notch stresses are assessed based on both the fictitious weld toe radius and the addition of measured actual notch radius to the fictitious radius. While no large differences are observed between the results of methods, the former one is found to be more practical and faster to implement from the end-user point of view.

  • 122138. Yildirim, H. C.
    et al.
    Marquis, Gary
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Aalto University, Finland .
    Sonsino, C. M.
    Lightweight potential of welded high-strength steel joints from S700 under constant and variable amplitude loading by high-frequency mechanical impact (HFMI) treatment2015In: Procedia Engineering, 2015, no C, p. 467-475Conference paper (Refereed)
    Abstract [en]

    Investigations with longitudinal stiffeners of the steel grade S700 under fully-reversed, constant amplitude loading and under variable amplitude loading with a straight-line spectrum show impressive fatigue strength improvement by high-frequency mechanical impact (HFMI) treatment. However, the degree of improvement was for variable amplitude loading lower when compared to constant amplitude loading due to local plasticity which occurs during larger load levels and consequently reduces the beneficial compressive residual stresses. Apart from the HFMI-treatment, the exceedance of constant amplitude loading (Woehler-lines) by variable amplitude loading (Gassner-lines) offers further lightweight potential, despite the lower degree of improvement by HFMI under spectrum loading.

  • 122139. Yildirim, Halid Can
    et al.
    Leitner, Martin
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Department of Applied Mechanics, School of Engineering, Aalto University, Aalto, Finland.
    Stoschka, Michael
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Department of Aerospace Engineering, Khalifa University of Science, Technology and Research (KUSTAR), P.O. Box: 127788, Abu Dhabi, United Arab Emirates.
    Application studies for fatigue strength improvement of welded structures by high-frequency mechanical impact (HFMI) treatment2016In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 106, p. 422-435Article in journal (Refereed)
    Abstract [en]

    In 2013, a new guideline for the design of high-frequency mechanical impact (HFMI) treatment was drafted. The proposed design curves were made based on the fatigue data of axially-loaded welded joints which were manufactured from high-strength steels. All the S-N curves were shown to be conservative with respect to the existing fatigue data for laboratory-scale specimens of longitudinal, transverse, and butt welds. In reality, structures in civil, offshore, mechanical engineering and ship industries generally include large-scale and more complicated components rather than laboratory-scale specimens. Therefore, this paper firstly presents the validation of design proposals by considering fatigue data sets for large-scale welded structures. In total, 62 fatigue data points for bridge, crane and beam-like components are reported, in which the yield strength varies from 250 to 725 MPa, and stress ratio varies from -1 to 0.56. Validations are then extended also for cover plates by performing fatigue tests of 23 weld details both in as-welded and HFMI-treated cases for the use of crane industry. Both the extracted and obtained fatigue data are found to be in good agreement with the previously-proposed design guidelines for nominal and effective notch stress assessment.

  • 122140. Yildirim, Halid Can
    et al.
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    A round robin study of high-frequency mechanical impact (HFMI)-treated welded joints subjected to variable amplitude loading2013In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 57, no 3, p. 437-447Article in journal (Refereed)
    Abstract [en]

    High-frequency mechanical impact (HFMI) treatment has been significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded structures. The development of an International Institute of Welding best practice guideline for implementing HFMI has been hindered by the lack of directly comparable experimental data for numerous HFMI methods. In this study, nominally identical longitudinal attachments in high-strength steel were manufactured in one welding workshop and distributed to four HFMI equipment manufacturers for treatment. Specimens were fatigue tested on a machine using identical variable amplitude loading histories. HFMI groove measurements were done for each specimen and X-ray diffraction-based residual stress measurements were performed on 10 specimens. The HFMI groove dimensions and the residual stress states showed similarity in general, however small changes were observed. Experimental results indicate that all of the HFMI-improved welds from the HFMI equipment manufacturers satisfied the previously proposed characteristic S-N line based on both the yield strength and the specimen geometry. Results of the study are valuable and promising with respect to the development of a future guideline. The goal of the study has not been to compare treatments, so specific data points are not associated specific HFMI equipment manufacturers.

  • 122141. Yildirim, Halid Can
    et al.
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue design of axially-loaded high frequency mechanical impact treated welds by the effective notch stress method2014In: Materials and Design, ISSN 0261-3069, Vol. 58, p. 543-550Article in journal (Refereed)
    Abstract [en]

    The effective notch stress method (ENS) as defined by the International Institute of Welding is widely used by design engineers to assess the fatigue strength of welded components. This paper provides a comprehensive evaluation of published data for welded joints improved by high frequency mechanical impact (HFMI) treatment. The goal is to verify already-known fatigue classes for the ENS with the available axially-loaded fatigue data. In total, 280 experimental test results obtained from longitudinal, cruciform and butt welds subject to stress ratio of R = 0.1 axial loading are evaluated. Notch stress concentration factors (K-n) for each joint geometry are analysed based on the finite element method. Calculated K-n and reported nominal stress values are used to determine local stresses. Fatigue strength assessment of the all available data is performed by the previously-proposed and verified correction procedure for yield strength (f(y)). A formerly-defined minimum K-n values as a function of f(y) is used for butt welds. The already-known fatigue classes are found to be conservative with respect to available fatigue test data.

  • 122142. Yildirim, Halid Can
    et al.
    Marquis, Gary B.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Aalto University, Finland.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Fatigue assessment of high frequency mechanical impact (HFMI)-improved fillet welds by local approaches2013In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, p. 57-67Article in journal (Refereed)
    Abstract [en]

    Local fatigue assessment methods like the structural hot spot stress and effective notch stress methods as defined by the International Institute of Welding are widely used by design engineers and researchers to assess the fatigue strength of welded components. This paper provides a comprehensive evaluation of published data for welded joints which had been improved using high frequency mechanical impact (HFMI) treatment. All of the published data for HFMI-treated welds are presented in terms of nominal stress. The goal of the current paper is to establish local fatigue assessment procedures for improved fillet welds. In total, 160 published experimental results for longitudinal and cruciform welds subjected to R = 0.1 axial loading are evaluated. Local stress quantities for each joint were assessed based on the finite element analyses and reported nominal stress values. A correction procedure for yield strength that was previously verified for nominal stress-based fatigue assessment is also applied to the local stress methods studied in this paper. For both the structural hot spot stress and effective notch stress methods, sets of characteristic fatigue strength curves as functions of yield strength are proposed and verified. The structural hot spot stress method includes one set of fatigue strength curves for load-carrying welds and a second set for non-load carrying welds. The effective notch stress method includes a single set of curves for all welds. All of the design curves proposed in this study are conservative with respect to available fatigue test data.

  • 122143. Yildirim, H.C.
    et al.
    Marquis, Gary
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Department of Applied Mechanics, Aalto University, Finland.
    Fatigue data of High-Frequency Mechanical Impact (HFMI) improved welded joints subjected to overloads2015In: Analysis and Design of Marine Structures: Proceedings of the 5th International Conference on Marine Structures, MARSTRUCT 2015, 2015, p. 317-322Conference paper (Refereed)
    Abstract [en]

    In the past decade, High Frequency Mechanical Impact (HFMI) has significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded steel structures. The evaluation and features of developing guideline within the International Institute of Welding (IIW) for the design of structures improved using HFMI is briefly discussed. So far, the extra fatigue strength benefit for HFMI-treated high strength steels has been mostly shown for constant amplitude loading. This paper reports 68 available HFMI-improved welds subjected to overloads or pre-fatigue loads at various loading conditions prior to fatigue testing. These loading conditions are often seen for marine structures.

  • 122144.
    Yildirim, Siho
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Rashid, Omar
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Effektivisering av teknikhusens grundläggningar längs järnvägar: Ett arbete som behandlar behovet om att effektivisera standarden för grundläggningen av ett teknikhus.2017Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Trafikverket is responsible for one of Sweden’s largest infrastructure project, namely replacing the current signal system along the countries railway to ERTMS. With the replacement of the signal system comes the need to replace 1 500 equipment shelters. The task is to analyze costs for the equipment shelter’s current foundation standard and try to find cheaper solutions. The work is mainly executed by analyzing alternative materials and foundations, but also manufacturing, installation, logistics, impacting loads and geology. One of the goals is to reduce the current costs of the project, and the main task is to find a new foundation standard that Trafikverket can use for future equipment shelters. The most common foundation types for equipment shelters turned out to be crawling spaces and plinth foundations out of sheet-metal and concrete. The report also presents ground screws, which is a new idea for equipment shelters. The report’s conclusion is that ground screws are the cheapest and most flexible foundation for equipment shelters. Even sheet-metal frames, which are a more common option today, proved to be a more economical choice than the current standard. The total saving turned out to be near 34 million SEK with ground screws and therefore one of the objectives has been achieved. The main goal of possibly finding a new standard, however, requires future investigations by Trafikverket before it can be determined possible.

    A recommendation to Trafikverket is to further investigate the price of foreign suppliers’ ground screws and determine if the installation is to be carried out on its own. For further studies, a detailed cost analysis of cantilevered houses and transports is recommended.

  • 122145.
    Yildirimdemir, Oytun
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Utformning av Distributionsflöde samt returflöde av defekta produkter i Turkiet: En fallstudie på företaget Axis Communications AB2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Axis is one of the world's largest providers of network based surveillance cameras with partners in 179 countries. Axis has over the past years experienced a deterioration of sales growth in the Turkish market despite forecasts showing high market potential. In mean time Axis´s distributor and retailer have expressed dissatisfaction with Axis´s processes for import and handling of faulty units. Therefore the research was designed to map the processes for importation into Turkey and process for faulty units handling, to get an objective view of the situation and suggest potential improvements. Mapping of Axis's processes in Turkey has been done and based on Just--‐In--‐Time and Supply Chain Management literature the research has found potential non--‐value adding activities. Axis has been recommended to introduce new performance measurement points to be able to follow up and improve the importation and faulty units handling in Turkey, and eventually eliminate these non--‐value adding activities. Suggested measurements: • Ratio between the value of goods shipped and administrative costs for its imports. • The lead--‐time for the distributor to replace a faulty unit from its first encounter with customer. With help of these measurements initiatives can easier be taken and action be made to improve the situation. Some suggestions for improvements are:

    • Consolidation of shipments, see Figure 7 and 8 (p. 19), for low ratio on value goods and administrative expenses . •

    Delivery of import documents directly to the distributor in parallel with the shipment of the goods to avoid delays at customs.

    Keep a limited inventory for replacement of defective products for quick replacement.

  • 122146.
    Yildiz, Ahmet Bahadir
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Weidow, Jonathan
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Ryukhtin, Vasyl
    Nucl Phys Inst, Cp 130, Husinec Rez 25068, Czech Republic..
    Norgren, Susanne
    Sandvik, SE-12680 Stockholm, Sweden.;Uppsala Univ, Dept Engn Sci, Appl Mat Sci, SE-75121 Uppsala, Sweden..
    Wahnström, Göran
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Very-small angle neutron scattering study on grain coarsening inhibition by V-doping of WC-Co composites2019In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 173, p. 106-109Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of cemented carbides can be tuned by controlling WC grain coarsening and the simultaneous growth of the binder pocket size during the sintering. So far, bulk studies considering this phenomenon are scarce, but here, we report the first very-small angle neutron scattering (VSANS) study on cemented carbides. VSANS is supplemented with electron backscatter diffraction (EBSD) and the microstructural refinement by increasing V-doping (0, 0.02, 022, and 0.76 wt%) is quantified. The capability of VSANS as a non-destructive bulk probe for cemented carbides is shown, paving way for forthcoming in-situ studies.

  • 122147.
    Yildiz, Erdem
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Mögelrisker i Sverige olika år gentemot standardklimat: En jämförelse hur olika geografiska platser med olika klimat har olika mögelrisker gentemot alla modeller som baseras på standardklimat.2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 122148. Yildiz, Hasan
    et al.
    Forsberg, Rene
    Ågren, Jonas
    Tscherning, J
    Sjöberg, Lars E.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Comparison of remove-compute-restore and least squares modification of Stokes' formula techniques to quasi-geoid determination over the Auvergne test area2012In: Journal of Geodetic Science, ISSN 2081-9919, E-ISSN 2081-9943, Vol. 2, no 1, p. 53-64Article in journal (Refereed)
    Abstract [en]

    The remove-compute-restore (RCR) technique for regional geoid determination implies that both topography and low-degree global geopotential model signals are removed before computation and restored after Stokes' integration or Least Squares Collocation (LSC) solution. The Least Squares Modification of Stokes' Formula (LSMS) technique not requiring gravity reductions is implemented here with a Residual Terrain Modelling based interpolation of gravity data. The 2-D Spherical Fast Fourier Transform (FFT) and the LSC methods applying the RCR technique and the LSMS method are tested over the Auvergne test area. All methods showed a reasonable agreement with GPS-levelling data, in the order of a 3-3.5 cm in the central region having relatively smooth topography, which is consistent with the accuracies of GPS and levelling. When a 1-parameter fit is used, the FFT method using kernel modification performs best with 3.0 cm r.m.s difference with GPS-levelling while the LSMS method gives the best agreement with GPS-levelling with 2.4 cm r.m.s after a 4-parameter fit is used. However, the quasi-geoid models derived using two techniques differed from each other up to 33 cm in the high mountains near the Alps. Comparison of quasi-geoid models with EGM2008 showed that the LSMS method agreed best in term of r.m.s.

  • 122149.
    Yildiz, Mustafa
    KTH, School of Electrical Engineering and Computer Science (EECS).
    On more electric airplane: case study Stockholm-Copenhagen2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In parallel to growing global population, the amount of people traveling around the worldalso increases. This pushes the industry to develop more energy efficient vehicles. Theconcept of electrification of vehicles has been adopted by the aviation industry in orderto reduce environmental impacts and lower operating costs. Although much research hasbeen done on various more electric airplanes, almost all of them are conducted only forone subsystem, lacking the aim of optimizing the total energy outtake from the enginesby all subsystems. This report aims to fill this gap by applying optimization techniquesto systematically decide when novel technologies are worthwhile, in terms of energy efficiency.Hence, the goal of this report is to develop a methodology for evaluating whendifferent MEA technologies are beneficial to implement in future airplanes. In this proposedapproach, a Matlab model has been developed which takes publicly available nonpropulsivepower demands and efficiencies of various subsystems into account, integratesthose with real flight data of a case study, and as a result gives the user a comparison of nonpropulsivefuel burn, being 1088.5 kg for conventional, 756.5 kg for more-electric, and 351.5kg for all-electric architectures, depending on the level of electrification. The difference intotal fuel burn between the conventional and all electric cases, including fuel consumptionfor propulsion, represents a reduction of total fuel burn on the order of 10 percent. Sinceas many electrical loads as possible are integrated into the proposed approach, this modelcan also be used for generator sizing as discussed in the results section of the case study.

  • 122150. Yilmaz, E.
    et al.
    Ramström, Olof
    KTH, Superseded Departments, Chemistry.
    Moller, P.
    Sanchez, D.
    Mosbach, K.
    A facile method for preparing molecularly imprinted polymer spheres using spherical silica templates2002In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 12, no 5, p. 1577-1581Article in journal (Refereed)
    Abstract [en]

    A novel and facile preparation method for spherical molecularly imprinted polymer (MIP) beads is presented. Two types of beads were synthesized and investigated: (i) silica-MIP composites were obtained by filling spherical, porous C-4-coated silica beads with print molecule and monomers followed by polymerisation; (ii) spherical molecularly imprinted polymer beads were acquired mirroring the silica particles in size, shape and pore structure by removing the silica matrix from the silica-MIP composites. With regard to their chromatographic properties and yield of the materials both types of particle were more advantageous compared to irregularly shaped traditional MIPs. Also the work-up time to obtain imprinted spherical particles is greatly reduced compared to traditional methods using polymer monoliths, which have to be ground, sieved and sedimented. Generally, the described method may open new possibilities for synthesis of novel types of imprinted polymer formats such as membranes, bulk polymers, films or in-situ columns using appropriate support or sacrificial materials.

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