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  • 126501. Zhu, K.
    et al.
    Rahimi, S.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Zhang, B.
    Design phasor data concentrator as adaptive delay buffer for wide-area damping control2015In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 127, p. 22-31Article in journal (Refereed)
    Abstract [en]

    Phasor Data Concentrators (PDCs) are employed to aggregate data frames from multiple Phasor Measurement Units (PMUs) with the same time-stamp into data packets. This function is an essential step in the utilization of PMU data in Wide-Area Monitoring and Control (WAMC) system. This is facilitated by assigning a fixed and heuristically decided wait time to the PDC buffer. The processed PMU data packets are sent to WAMC applications or similarly PDCs at higher hierarchies in the WAMC system when either a PDC buffer is full or its wait time has passed. In this paper, two methods to configure adaptive PDC wait time based on recent PMU traffic delay patterns are proposed. The purpose is to reduce the frequency of performing delay compensations in wide-area damping control system. With the adaptive PDC delay buffer in place, the wide-area damping controller only switches its gain once every five seconds, given the studied PMU traffic delay scenarios, instead of the current practice which requires the control gain to be adapted on a per PMU data frame basis, e.g., 50 or 60 times every second. The proposed methods offer a perspective to efficiently utilize the supporting Information and Communication Technology infrastructure with the purpose to simplify the design and implementation of wide-area damping control system.

  • 126502.
    Zhu, Kai
    et al.
    Tianjin Univ Commerce, Tianjin Key Lab Refrigerat Technol, Tianjin 300134, Peoples R China..
    Li, Xueqiang
    Tianjin Univ Commerce, Tianjin Key Lab Refrigerat Technol, Tianjin 300134, Peoples R China.;Tianjin Univ, Sch Environm Sci & Engn, Tianjin 300350, Peoples R China.;Malardalen Univ, Sch Business Soc & Engn, SE-72123 Vastras, Sweden..
    Campana, Pietro Elia
    Malardalen Univ, Sch Business Soc & Engn, SE-72123 Vastras, Sweden.;KTH Royal Inst Technol, Sch Chem Sci & Engn, SE-10044 Stockholm, Sweden..
    Li, Hailong
    Tianjin Univ Commerce, Tianjin Key Lab Refrigerat Technol, Tianjin 300134, Peoples R China.;Malardalen Univ, Sch Business Soc & Engn, SE-72123 Vastras, Sweden..
    Yan, Jinyue
    KTH, School of Chemical Science and Engineering (CHE). Malardalen Univ, Sch Business Soc & Engn, SE-72123 Vastras, Sweden.
    Techno-economic feasibility of integrating energy storage systems in refrigerated warehouses2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 216, p. 348-357Article in journal (Refereed)
    Abstract [en]

    This work evaluates the techno-economic feasibility of integrating the cold energy storage system and the electrical energy storage system in a refrigerated warehouse for shifting the power consumption. A dynamic model has been developed in TRNSYS (R). Based on the dynamic simulation, the performance and benefit of those two types of energy storage systems were compared. Results showed that, the integration of a cold energy storage can reduce the electricity consumption and operational cost by 4.3% and 20.5%, respectively. Even though integrating a battery system will increase the electricity consumption by 3.9%, it can reduce the operational cost by 18.7%. The capacity of the energy storage systems, the battery price and the peak electricity price had been identified as key parameters affecting the performance and benefit. To achieve a payback period less than 3 year, for the integration of a cold energy storage system, the peak electricity price should be increased by 25% from the current level, while for the integration of a battery system, the battery price should drop to 0.7 kRMB/kWh.

  • 126503.
    Zhu, Kaixin
    KTH, School of Engineering Sciences (SCI), Physics.
    Nuclear Reactor Seismic Analysis Considering Soil-Structure Interaction2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 126504.
    Zhu, Kun
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Data Quality in Wide-Area Monitoring and Control Systems: PMU Data Latency, Completness, and Design of Wide-Area Damping Systems2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The strain on modern electrical power system operation has led to an ever increasing utilization of new Information Communication Technology (ICT) systems to enhance the reliability and efficiency of grid operation. Among these proposals, Phasor Measurement Unit (PMU)-based Wide-Area Monitoring and Control (WAMC) systems have been recognized as one of the enablers of “Smart Grid”, particularly at the transmission level, due to their capability to improve the real-time situational awareness of the grid. These systems differ from the conventional Supervisory Control And Data Acquisition (SCADA) systems in that they provide globally synchronized measurements at high resolutions. On the other hand, the WAMC systems also impose several stringent requirements on the underlying ICT systems, including performance, security, and availability, etc. As a result, the functionality of the WAMC applications is heavily, but not exclusively, dependent on the capabilities of the underlying ICT systems. This tight coupling makes it difficult to fully exploit the benefits of the synchrophasor technology without the proper design and configuration of ICT systems to support the WAMC applications. The strain on modern electrical power system operation has led to an ever increasing utilization of new Information Communication Technology (ICT) systems to enhance the reliability and efficiency of grid operation. Among these proposals, Phasor Measurement Unit (PMU)-based Wide-Area Monitoring and Control (WAMC) systems have been recognized as one of the enablers of “Smart Grid”, particularly at the transmission level, due to their capability to improve the real-time situational awareness of the grid. These systems differ from the conventional Supervisory Control And Data Acquisition (SCADA) systems in that they provide globally synchronized measurements at high resolutions. On the other hand, the WAMC systems also impose several stringent requirements on the underlying ICT systems, including performance, security, and availability, etc. As a result, the functionality of the WAMC applications is heavily, but not exclusively, dependent on the capabilities of the underlying ICT systems. This tight coupling makes it difficult to fully exploit the benefits of the synchrophasor technology without the proper design and configuration of ICT systems to support the WAMC applications.

    In response to the above challenges, this thesis addresses the dependence of WAMC applications on the underlying ICT systems. Specifically, two of the WAMC system data quality attributes, latency and completeness, are examined together with their effects on a typical WAMC application, PMU-based wide-area damping systems. The outcomes of this research include quantified results in the form of PMU communication delays and data frame losses, and probability distributions that can model the PMU communication delays. Moreover, design requirements are determined for the wide-area damping systems, and three different delay-robust designs for this WAMC application are validated based on the above results. Finally, a virtual PMU is developed to perform power system and communication network co-simulations.

    The results reported by this thesis offer a prospect for better predictions of the performance of the supporting ICT systems in terms of PMU data latency and completeness. These results can be further used to design and optimize the WAMC applications and their underlying ICT systems in an integrated manner. This thesis also contributes a systematic approach to design the wide-area damping system considering the PMU data latency and completeness. Finally, the developed virtual PMU, as part of a co-simulation platform, provides a means to investigate the dependence of WAMC applications on the capabilities of the underlying ICT systems in a cost-efficient manner.

  • 126505.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Al-Hammouri, A. T.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    To concentrate or not to concentrate: Performance analysis of ICT system with data concentrations for Wide-area Monitoring and Control Systems2012In: Power and Energy Society General Meeting, 2012 IEEE, IEEE , 2012, p. 6344977-Conference paper (Refereed)
    Abstract [en]

    Timely and synchronized phasor data at high resolutions holds great promise for more responsible and advanced power grid operations. It is expected that combined effort of developing new application paradigms and the supporting Information and Communication Technology (ICT) will enable the miracle of Smart Grid at the transmission level. This paper addresses the design of the supporting ICT system for Wide Area Monitoring and Control applications from the performance perspective. The major contribution that distinguishes this paper from previous research efforts in the same area is that this study quantifies the end-to-end data delay with consideration of different levels of data concentrations. The analysis performed in this paper is not limited to the delay caused by individual ICT components but also provides means to view and analyze the delay of the entire supporting ICT system. Moreover, the quantified delay results drawn in this paper will potentially provide valuable input to the discussion on the coming standards for synchronized phasor measurements.

  • 126506.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Wu, Yiming
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Design of Robust Wide-Area Damping Controller Based on Synchronized Phasor2012In: The 9th International Conference on Advances in Power System Control, Operation & Management (APSCOM 2012), 18 November-21 November 2012, Kowloon Shangri-La Hotel, Hong Kong: Conference Handbook, Hongkong: Institution of Engineering and Technology, 2012Conference paper (Refereed)
  • 126507.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    König, Johan
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Analysis of data quality issues in wide area monitoring and control systems2010In: 2010 IREP Symposium - Bulk Power System Dynamics and Control - VIII, IREP2010, Rio de Janeiro, 2010Conference paper (Refereed)
    Abstract [en]

    Synchronized phasor measurement based Wide Area Monitoring and Control (WAMC) system is becoming a reality with international research and development both in academia and industry. Timely and accurate data with high resolutions holds great promise for more responsible and advanced grid control and operation. Currently, most of the research focuses on the different control schemes and applications. A relatively less addressed aspect is the dependency of the WAMC system on the performance of the Information and Communication Technology (ICT) infrastructure, without whose support the projected functionalities of the WAMC systems will not be achieved. Possible input delay brought by the complex data transfer and processing processes in WAMC systems are presented at the beginning of this paper. Thereafter, simulations where delayed phasor measurements are fed to a typical WAMC application - Static Var Compensation (SVC) are conducted iteratively to detect its maximum tolerated delay. Based on this maximum tolerated delay, the consequences of missing certain data in the phaor packets have been studied. Furthermore, data quality requirements to design a reliable SVC function are analyzed based on simulation results. In conjunction with the requirement discussion, the paper is concluded by proposing a robust ICT architecture to mitigate the aforementioned data quality issues.

  • 126508.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    König, Johan
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Data quality and reliability aspects of ICT infrastructures for Wide Area Monitoring and Control Systems2010In: 2010 5th International Conference on Critical Infrastructure, CRIS 2010, Beijing, 2010Conference paper (Refereed)
    Abstract [en]

    Synchronized phasor measurement based Wide Area Monitoring and Control (WAMC) system is becoming a reality within international research and development both in academia and industry. Timely and accurate data with high resolutions holds great promise for more responsible and advanced grid control and operation. Currently, most of the research focuses on the different control schemes and applications. A relatively less addressed aspect is the dependency of the WAMC system on the performance of the Information and Communication Technology (ICT) infrastructure, without whose support the projected functionalities of the WAMC systems will be not achieved. Possible delays brought by the complex data transfer and processing processes in WAMC systems are addressed in the first part of this paper. Thereafter, simulations where delayed Phasor measurements are fed to a typical WAMC application - Static Var Compensation (SVC) are conducted iteratively to detect its maximum tolerated delay. Furthermore, performance requirements to design a reliable SVC function are analyzed based on simulation results. In conjunction with the requirement discussion, a robust ICT architecture is proposed to mitigate the data latency and incompleteness issue. The paper is concluded by addressing data quality issues relating to the remote signal based SVC controller system reliability.

  • 126509.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    ICT architecture impact on wide area monitoring and control systems' reliability2011In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 26, no 4, p. 2801-2808Article in journal (Refereed)
    Abstract [en]

    Timely and accurate data with high resolutions holds great promise for more responsible and advanced power grid operations. The research has been focusing on design of monitoring and control scheme given the assumptions that the supporting information and communication technology (ICT) systems are capable of providing data and perform control with sufficient quality. A relatively less addressed aspect is the dependency of wide-area monitoring and control (WAMC) systems on their supporting ICT architecture which is usually a compromise between various concerns, such as data quality, interoperability, or security. Without an appropriate ICT architecture design, the projected WAMC system functionalities run the risk of being jeopardized. This paper begins with a presentation about possible delays brought by complex data-transfer and processing processes. Analytical experiments are conducted with purposes to quantify the maximum delay and input signal's sensitivity toward delay on a typical WAMC application where the control of static var compensation (SVC) is coordinated with generator excitations using phasor measurements. Given the characteristics of this particular control scheme, two possible ICT architectures that provide data with different qualities are compared concerning the reliability of this WAMC application. This paper concludes by proposing a generic ICT architecture, enabling efficient WAMC systems implementation in terms of data quality.

  • 126510.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    ICT system performance impact on wide area monitoring and control systems2012In: 44th International Conference on Large High Voltage Electric Systems 2012, 2012, p. 1-10Conference paper (Refereed)
    Abstract [en]

    Timely and accurate data with high resolutions holds great promise for more responsible and advanced power grid operations. The research has been focusing on design of monitoring and control scheme given assumptions that the supporting Information and Communication Technology (ICT) systems are capable to provide data and perform control with sufficient quality. A relatively less addressed aspect is the dependency of Wide area monitoring and control (WAMC) systems on their supporting ICT architecture which is usually a compromise between various concerns, such as data quality, interoperability or security. Without an appropriate ICT architecture design, the projected WAMC system functionalities run the risk of being jeopardized. This paper begins with a presentation about possible delays brought by complex data transfer and processing processes. Analytical experiments are conducted with purposes to quantify the maximum delay and input signal's sensitivity towards delay on a typical WAMC application where the control of Static Var Compensation (SVC) is coordinated with generator excitations using phasor measurements. Given the characteristics of this particular control scheme, two possible ICT architectures that provide data with different qualities are compared concerning the reliability of this WAMC application. The paper is concluded by proposing a generic ICT architectures enabling efficient WAMC systems implementation in terms of data quality.

  • 126511.
    Zhu, Kun
    et al.
    Ventyx ABB Co, S-10044 Vasteras, Sweden.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Holmström, Sture
    Ericsson, Göran
    Design Requirements of Wide-Area Damping Systems-Using Empirical Data From a Utility IP Network2014In: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 5, no 2, p. 829-838Article in journal (Refereed)
    Abstract [en]

    Phasor Measurement Unit (PMU) communication delays and data frame losses play a critical role in designing of wide-area damping systems driven by synchrophasor technology. While there are a plethora of simulation-based studies addressing this issue, empirical results from actual PMUs deployed in the field are rare. This paper provides important insights into the characterization of PMU communication delays and data frame losses based on empirical results collected from a utility IP network. Additionally, efforts are also made to elicit design requirements considering the above PMU data quality problems. Furthermore, three distinct delay-robust wide-area damping control schemes parameterized according to the proposed requirements are validated against the empirical delays and data frame losses. Time-domain simulation results suggest that the control schemes in question can effectively stabilize the power system in all of the tested scenarios.

  • 126512.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Holmström, Sture
    Erisson, Göran
    An Empirical Study of Synchrophasor Communication Delay in a Utility TCP/IP Network2013In: International Journal of Emerging Electric Power Systems, ISSN 2194-5756, E-ISSN 1553-779X, Vol. 14, no 4, p. 341-250Article in journal (Refereed)
    Abstract [en]

    Although there is a plethora of literature dealing with Phasor Measurement Unit (PMU) communication delay, there has not been any effort to generalize empirical delay results by identifying the distributions with the best fit. The existing studies typically assume a distribution, or simply build on analogies to communication network routing delay. Specifically, this study provides insight into the characterization of the communication delay of both unprocessed PMU data and synchrophasors sorted by a Phasor Data Concentrator (PDC). The results suggest that a bi-modal distribution containing two normal distributions offers the best fit of the delay of the unprocessed data, whereas the delay profile of the sorted synchrophasors resembles a normal. Based on these results, the possibility of evaluating the reliability of a synchrophasor application with respect to a particular choice of PDC timeout is discussed.

  • 126513.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Deo, Samarth
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Al-Hammouri, Ahmad
    Jordan University of Science and Technology.
    Honeth, Nicholas
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Lars, Nordström
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Test platform for synchrophasor based wide-area monitoring and control applications2013In: Power and Energy Society General Meeting (PES), 2013 IEEE, Vancouver: IEEE , 2013, p. 6672308-Conference paper (Refereed)
    Abstract [en]

    Synchrophasor technology is considered as a main enabler for the envisioned Smart Grid at the transmission level. Despite some preliminary field test results reported from China Southern Grid, the majority of the synchrophasor applications are still in the engineering or advanced laboratory tests phases. One possible impedance of any real-life adoption of such applicationsis a lack of test platforms that are able to verify the proposed application paradigms in cost efficient manners, and also to demonstrate the interactions between the power system and the supporting ICT systems with sufficient details. In this paper, we report on the continuing research efforts targeting at developing a test platform for the development of the synchrophasor based applications. The platform incorporates a virtual Phasor Measurement Unit (PMU), a real-time simulator for power systems, a real-time simulator for communication networks, and an implementation of an open-source Phasor Data Concentrator. Specifically, this article focuses on the implementation and verification of the virtual PMU, and on the extension of its functionality to incorporate communication over UDP.

  • 126514.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Honeth, Nicholas
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Xu, Yuan
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Investigation of data exchange requirements for cooperative grid planning and operation2011Conference paper (Refereed)
    Abstract [en]

    IEC 61970 and 61968 together referred as Common Information Model (CIM), are proposed to facilitate integration of EMS applications with proprietary data formats and information exchange between control centers. To use Information and Communication Technology (ICT) systems in an optimized manner, it is necessary to partition the potentially voluminous data into subsets given their sources, expected exchange frequency, and subscribing applications. In response to these requirements, the concept of CIM profiles is brought up by CIMug. In this paper, functions illustrating the dependency between exchange data volume and basic grid parameters for each data profile are presented. A CIM/XML/RDFfile for a commonly available 40 bus test system modeled according to CIM 13 together with examples provided by standards are used as references. The method is validated by estimating the CIM/XML/RDF file sizes of similarly available 100 bus and 60 bus test systems. The contribution of this paper is that it provides ICT system designers with a means to estimate the corresponding requirements for various CIM based data exchange scenarios. The estimations are performed based on commonly known grid parameters such as number of buses, branches, generators, transformers and loads.

  • 126515.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Design of wide-area damping systems based on the capabilities of the supporting Information Communication Technology infrastructure2014In: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 8, no 4, p. 640-650Article in journal (Refereed)
    Abstract [en]

    The dependence of the functionality of the wide-area monitoring and control (WAMC) systems on the capabilities of their underlying Information Communication Technology (ICT) infrastructure indicates that the parameterisation of the WAMC application algorithm should be coordinated with the design of the supporting ICT system. This study presents a systematic approach to design wide-area damping systems considering phasor measurement unit (PMU) communication delays and data frame losses. The proposed design method is applied to calibrate a wide-area damping system based on generalised predictive control (GPC) for demonstration purposes. In addition, a framework to guide the parameterisation of the GPC- based wide-area damping system is also provided. This research offers a better perspective to predict the capabilities of the underlying ICT infrastructure in the WAMC systems. Moreover, the proposed design method can be generalised to design delay-robust damping systems with compensation limits. Finally, it also offers an opportunity to associate the parameterisation of the damping system with the capabilities of its supporting ICT infrastructure and the reliability of the intended damping control function.

  • 126516.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Ekstam, Lennart
    Application and analysis of Optimum PMU Placement methods with application to State Estimation Accuracy2009In: 2009 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, VOLS 1-8, New York: IEEE , 2009, p. 580-586Conference paper (Refereed)
    Abstract [en]

    Phasor measurement units (PMU) coupled with high speed and bandwidth communication infrastructure holds great promise for future power system control and operation. The geographic location of the PMUs within the power system naturally affects the value added by PMUs to one specific application in power grid control and operation. Optimization of placement has been the subject of much analysis and research. This paper compares one PMU placement method targeting enhancement of state estimation accuracy with the current PMU deployment method utilized in Svenska Kraftnat (SvK), the Swedish Transmission System Operator. The possible estimation improvement applying this optimum placement algorithm is further studied while more PMUs are involved. Considering that the deployment of PMUs within SvK's grid is still limited, the study has been performed in a simulation environment. The paper contains a brief description of the simulation platform and the assumptions made during the work as well. The analysis shows that there are considerable gains to be made in estimator accuracy if the PMUs are placed in accordance with this method when compared to the current placement strategy. It could also be observed when the PMU monitored buses reaches a certain number in the entire network, the further introduction of phasor measurements will not be as effective in estimation accuracy improvement.

  • 126517.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Hammouri, A.
    Jordan University of Science and Technology .
    Examination of data delay and packet loss for wide-area monitoring and control systems2012In: 2012 IEEE International Energy Conference and Exhibition, ENERGYCON 2012, IEEE , 2012, p. 927-934Conference paper (Refereed)
    Abstract [en]

    Timely and synchronized phasor data at high resolutions holds a great promise for more responsible and advanced power grid operations. It is expected that the combined effort of developing new application paradigms and the supporting Information and Communication Technology (ICT) will enable the evolutionary change for future transmission grid operation. This paper addresses the design of the supporting ICT system for Wide-Area Monitoring and Control applications considering system performance. The major contribution that distinguishes this paper from previous research efforts in the same area is that this study quantifies the end-to-end data delay and the received packet rate with considerations of different levels of data concentrations. The analysis performed in this paper is not merely limited to the performance issues caused by communication networks but also provides means to view and analyze the overall data delay of the entire supporting ICT system.

  • 126518. Zhu, Kun
    et al.
    Ou, Haiyan
    Fu, Hongyan
    Remb, Edvin
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Simple and Tunable Single-Bandpass Microwave Photonic Filter of Adjustable Shape2008In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 20, no 21-24, p. 1917-1919Article in journal (Refereed)
    Abstract [en]

    A simple and tunable single-hand pass microwave photonic filter of adjustable shape is proposed and experimentally demonstrated. The filter is based on multiple sources (spectrum-sliced by a Mach-Zehnder interferometer) and two cascaded incoherent optical structures, namely, a dispersion medium of 50-km single-mode fiber and a fiber ring delay line. In the experimental range from 1.0 to 3.8 GHz, a discretely tunable single-hand pass filter with a high Q-factor or a flat-top response is achieved by carefully matching the transfer functions of the two individual optical structures.

  • 126519. Zhu, Kun
    et al.
    Ou, Haiyan
    Ye, Chenhui
    Fu, Hongyan
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    All-optical coherence-free microwave filter with switchable passbands based on phase and intensity hybrid modulation2011In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 284, no 1, p. 140-143Article in journal (Refereed)
    Abstract [en]

    A simple all-optical coherence-free microwave notch filter is proposed and experimentally demonstrated. The filter with switchable passbands is based on a single-wavelength optical source and phase-intensity hybrid modulation scheme. The DC bias voltage applied to the Mach-Zehnder intensity modulator can be adjusted to switch signs of the tap coefficients, which affect the baseband response. Both lowpass and bandpass filtering responses are observed in the experiment and agree well with the simulated results.

  • 126520.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Song, Ji
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Chenine, Moustafa
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Analysis of phasor data latency in wide area monitoring and control systems2010In: 2010 IEEE International Conference on Communications Workshops, ICC 2010, Capetown, 2010Conference paper (Other academic)
    Abstract [en]

    Synchronized phasor measurement based Wide Area Monitoring and Control (WAMC) system is becoming a reality within international research and development both in academia and industry. Timely and accurate data with high resolutions holds great promise for more responsible and advanced grid control and operation. Currently, most of the research focuses on the different control schemes and applications. A relatively less addressed aspect is the dependency of the WAMC system on the performance of the Information and Communication Technology (ICT) infrastructure, without whose support the projected functionalities of the WAMC systems will be not achieved. Possible delays brought by the complex data transfer and processing processes in WAMC systems are addressed in the first part of this paper. Thereafter, simulations where delayed Phasor measurements are fed to the Static Var Compensator (SVC) are conducted iteratively to detect its maximum tolerated delay. Furthermore, performance requirements for the centralized computation and control actuation are researched and analyzed based on simulation results. It also includes a study on feasibility of compensations using local signal based Power System Stablizers (PSS) in situations with much phasor data delay. The paper is concluded by suggesting ICT architecture for WAMC systems aiming to improve its robustness.

  • 126521.
    Zhu, Kun
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Yuan, Xu
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Honeth, Nicholas
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Nordström, Lars
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Data Volume Estimation for CIM based Information Exchange2011Conference paper (Refereed)
    Abstract [en]

    IEC 61970 and 61968, which are commonly referred as Common Information Model (CIM), are proposed to facilitate integration of EMS applications and information exchange between EMS systems with propitiatory data structures. To use communication network in an optimized manner, it is necessary to partition the potentially voluminous data into subsets given their sources, expected exchange frequency, and subscribing applications. In response to these requirements, the concept of CIM profiles is brought up by CIMug. In this paper, functions illustrating the dependency between exchange data volume and basic grid parameters for each data profile are presented. A CIM/XML/RDF file for a generally available 40 bus test system (CIM 13) and examples provided by standards are used as references. The method is validated by estimating the data sizes of similarly available 100bus and 60bus test systems that are modeled according to CIM 13 as well. The contribution of this paper is that it provides ICT system designers with a means to estimate the corresponding requirements for various CIM/XML based data exchange patterns. The estimations are performed based on commonly known grid parameters such as number of buses, branches, generators, transformers and loads together with execution frequency of particular grid planning and operation applications.

  • 126522. Zhu, L.
    et al.
    Ang, C. Y.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Nguyen, K. T.
    Tan, S. Y.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhao, Y.
    Luminescent color conversion on cyanostilbene-functionalized quantum dots via in-situ photo-tuning2012In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 24, no 29, p. 4020-4024Article in journal (Refereed)
    Abstract [en]

    Photo-responsive CdSe quantum dots functionalized with the cyanostilbene unit are synthesized. The as-prepared quantum dot hybrid reveals a photo-tunable dual fluorescent characteristic. White light emission can be generated in situ from the hybrid through photoirradiation to adjust the relative intensities of the two complementary emissions. Luminescent color conversion through yellow, white, and blue can be realized by varying the photoirradiation time.

  • 126523.
    Zhu, Lailai
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical investigation of swimming micro-organisms in complex environments2012Licentiate thesis, comprehensive summary (Other academic)
  • 126524.
    Zhu, Lailai
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control.
    Simulation of individual cells in flow2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, simulations are performed to study the motion ofindividual cells in flow, focusing on the hydrodynamics of actively swimming cells likethe self-propelling microorganisms, and of passively advected objects like the red bloodcells. In particular, we develop numerical tools to address the locomotion ofmicroswimmers in viscoelastic fluids and complex geometries, as well as the motion ofdeformable capsules in micro-fluidic flows.

    For the active movement, the squirmer is used as our model microswimmer. The finiteelement method is employed to study the influence of the viscoelasticity of fluid on theperformance of locomotion. A boundary element method is implemented to study swimmingcells inside a tube. For the passive counterpart, the deformable capsule is chosen as the modelcell. An accelerated boundary integral method code is developed to solve thefluid-structure interaction, and a global spectral method is incorporated to handle theevolving cell surface and its corresponding membrane dynamics.

    We study the locomotion of a neutral squirmer with anemphasis on the change of swimming kinematics, energetics, and flowdisturbance from Newtonian to viscoelastic fluid. We also examine the dynamics of differentswimming gaits resulting in different patterns of polymer deformation, as well as theirinfluence on the swimming performance. We correlate the change of swimming speed withthe extensional viscosity and that of power consumption with the phase delay of viscoelasticfluids. Moreover, we utilise the boundary element method to simulate the swimming cells in astraight and torus-like bent tube, where the tube radius is a few times the cell radius. Weinvestigate the effect of tube confinement to the swimming speed and power consumption. Weanalyse the motions of squirmers with different gaits, which significantly affect thestability of the motion. Helical trajectories are produced for a neutralsquirmer swimming, in qualitative agreement with experimental observations, which can beexplained by hydrodynamic interactions alone.

    We perform simulations of a deformable capsule in micro-fluidic flows. We look atthe trajectory and deformation of a capsule through a channel/duct with a corner. Thevelocity of capsule displays an overshoot as passing around the corner, indicating apparentviscoelasticity induced by the interaction between the deformable membrane and viscousflow. A curved corner is found to deform the capsule less than the straight one. In addition, we propose a new cell sorting device based on the deformability of cells. Weintroduce carefully-designed geometric features into the flow to excite thehydrodynamic interactions between the cell and device. This interaction varies andclosely depends on the cell deformability, the resultant difference scatters the cellsonto different trajectories. Our high-fidelity computations show that the new strategy achievesa clear and robust separation of cells. We finally investigate the motion of capsule in awall-bounded oscillating shear flow, to understand the effect of physiological pulsation to thedeformation and lateral migration of cells. We observe the lateral migration velocity of a cellvaries non-monotonically with its deformability.

  • 126525.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    The motion of a deforming capsule through a corner2015In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 770, p. 374-397Article in journal (Refereed)
    Abstract [en]

    A three-dimensional deformable capsule convected through a square duct with a corner is studied via numerical simulations. We develop an accelerated boundary integral implementation adapted to general geometries and boundary conditions. A global spectral method is adopted to resolve the dynamics of the capsule membrane developing elastic tension according to the neo-Hookean constitutive law and bending moments in an inertialess flow. The simulations show that the trajectory of the capsule closely follows the underlying streamlines independently of the capillary number. The membrane deformability, on the other hand, significantly influences the relative area variations, the advection velocity and the principal tensions observed during the capsule motion. The evolution of the capsule velocity displays a loss of the time-reversal symmetry of Stokes flow due to the elasticity of the membrane. The velocity decreases while the capsule is approaching the corner, as the background flow does, reaches a minimum at the corner and displays an overshoot past the corner due to the streamwise elongation induced by the flow acceleration in the downstream branch. This velocity overshoot increases with confinement while the maxima of the major principal tension increase linearly with the inverse of the duct width. Finally, the deformation and tension of the capsule are shown to decrease in a curved corner.

  • 126526.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Do-Quang, Minh
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Locomotion by tangential deformation in a polymeric fluid2011In: Physical Reivew E, ISSN 1539-3755, Vol. 83, no 1, p. 011901-Article in journal (Refereed)
    Abstract [en]

    In several biologically relevant situations, cell locomotion occurs in polymeric fluids with Weissenberg number larger than 1. Here we present results of three-dimensional numerical simulations for the steady locomotion of a self-propelled body in a model polymeric (Giesekus) fluid at low Reynolds number. Locomotion is driven by steady tangential deformation at the surface of the body (the so-called squirming motion). In the case of a spherical squirmer, we show that the swimming velocity is systematically less than that in a Newtonian fluid, with a minimum occurring for Weissenberg numbers of order 1. The rate of work done by the swimmer always goes up compared to that occurring in the Newtonian solvent alone but is always lower than the power necessary to swim in a Newtonian fluid with the same viscosity. The swimming efficiency, defined as the ratio between the rate of work necessary to pull the body at the swimming speed in the same fluid and the rate of work done by swimming, is found to always be increased in a polymeric fluid. Further analysis reveals that polymeric stresses break the Newtonian front-back symmetry in the flow profile around the body. In particular, a strong negative elastic wake is present behind the swimmer, which correlates with strong polymer stretching, and its intensity increases with Weissenberg number and viscosity contrasts. The velocity induced by the squirmer is found to decay in space faster than in a Newtonian flow, with a strong dependence on the polymer relaxation time and viscosity. Our computational results are also extended to prolate spheroidal swimmers and smaller polymer stretching are obtained for slender shapes compared to bluff swimmers. The swimmer with an aspect ratio of two is found to be the most hydrodynamically efficient.

  • 126527.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Ecole Polytech Fed Lausanne, Lab Fluid Mech & Instabil, CH-1015 Lausanne, Switzerland.;Princeton Univ, Dept Mech & Aerosp Engn, Princeton, NJ 08540 USA.
    Gallaire, Francois
    Ecole Polytech Fed Lausanne, Lab Fluid Mech & Instabil, CH-1015 Lausanne, Switzerland..
    Bifurcation Dynamics of a Particle-Encapsulating Droplet in Shear Flow2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 6, article id 064502Article in journal (Refereed)
    Abstract [en]

    To understand the behavior of composite fluid particles such as nucleated cells and double emulsions in flow, we study a finite-size particle encapsulated in a deforming droplet under shear flow as a model system. In addition to its concentric particle-droplet configuration, we numerically explore other eccentric and time-periodic equilibrium solutions, which emerge spontaneously via supercritical pitchfork and Hopf bifurcations. We present the loci of these solutions around the codimension-two point. We adopt a dynamic system approach to model and characterize the coupled behavior of the two bifurcations. By exploring the flow fields and hydrodynamic forces in detail, we identify the role of hydrodynamic particle-droplet interaction which gives rise to these bifurcations.

  • 126528.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Low-Reynolds number swimming in a capillary tube2013In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 726, p. 285-311Article in journal (Refereed)
    Abstract [en]

    We use the boundary element method to study the low-Reynolds-number locomotion of a spherical model microorganism in a circular tube. The swimmer propels itself by tangential or normal surface motion in a tube whose radius is of the order of the swimmer size. Hydrodynamic interactions with the tube walls significantly affect the average swimming speed and power consumption of the model microorganism. In the case of swimming parallel to the tube axis, the locomotion speed is always reduced (respectively, increased) for swimmers with tangential (respectively, normal) deformation. In all cases, the rate of work necessary for swimming is increased by confinement. Swimmers with no force dipoles in the far field generally follow helical trajectories, solely induced by hydrodynamic interactions with the tube walls, and in qualitative agreement with recent experimental observations for Paramecium. Swimmers of the puller type always display stable locomotion at a location which depends on the strength of their force dipoles: swimmers with weak dipoles (small alpha) swim in the centre of the tube while those with strong dipoles (large alpha) swim near the walls. In contrast, pusher swimmers and those employing normal deformation are unstable and end up crashing into the walls of the tube. Similar dynamics is observed for swimming into a curved tube. These results could be relevant for the future design of artificial microswimmers in confined geometries.

  • 126529.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Self-propulsion in viscoelastic fluids: pushers vs. pullers2012In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, no 5, p. 051902-Article in journal (Refereed)
    Abstract [en]

    We use numerical simulations to address locomotion at zero Reynolds number in viscoelastic (Giesekus) fluids. The swimmers are assumed to be spherical, to self-propel using tangential surface deformation, and the computations are implemented using a finite element method. The emphasis of the study is on the change of the swimming kinematics, energetics, and flow disturbance from Newtonian to viscoelastic, and on the distinction between pusher and puller swimmers. In all cases, the viscoelastic swimming speed is below the Newtonian one, with a minimum obtained for intermediate values of the Weissenberg number, We. An analysis of the flow field places the origin of this swimming degradation in non-Newtonian elongational stresses. The power required for swimming is also systematically below the Newtonian power, and always a decreasing function of We. A detail energetic balance of the swimming problem points at the polymeric part of the stress as the primary We-decreasing energetic contribution, while the contributions of the work done by the swimmer from the solvent remain essentially We-independent. In addition, we observe negative values of the polymeric power density in some flow regions, indicating positive elastic work by the polymers on the fluid. The hydrodynamic efficiency, defined as the ratio of the useful to total rate of work, is always above the Newtonian case, with a maximum relative value obtained at intermediate Weissenberg numbers. Finally, the presence of polymeric stresses leads to an increase of the rate of decay of the flow velocity in the fluid, and a decrease of the magnitude of the stresslet governing the magnitude of the effective bulk stress in the fluid.

  • 126530.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rabault, Jean
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    The dynamics of a capsule in a wall-bounded oscillating shear flow2014Report (Other academic)
    Abstract [en]

    The motion of an initially spherical capsule in a wall-bounded oscillating shear flow is studied via an accelerated boundary integral implementation. Neo-Hookean model is used as the constitutive law of the membrane of capsule. The lateral migration velocity of the capsule varies non-monotonically with its capillary number. It is negatively related with the initial height of the capsule above the wall. A positive correlation between the lateral migration velocity and normal stress difference is identified. The correlation becomes strongest for the capsule with the highest lateral migration velocity. For a fixed capillary number, the lateral migration velocity decreases linearly with the frequency of oscillating shear, and approaches an asymptotic value of zero for high frequency. The deformation of capsule displays a wave-like variation in time and its frequency is twice that of the underlying shear. A phase delay is observed between the variation of capsule deformation with that of the oscillatory flow, more pronounced for a more deformable capsule.

     

  • 126531.
    Zhu, LaiLai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rabault, Jean
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Ecole Polytech, F-91128 Palaiseau, France.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    The dynamics of a capsule in a wall-bounded oscillating shear flow2015In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, no 7, article id 071902Article in journal (Refereed)
    Abstract [en]

    The motion of an initially spherical capsule in a wall-bounded oscillating shear flow is investigated via an accelerated boundary integral implementation. The neo-Hookean model is used as the constitutive law of the capsule membrane. The maximum wall-normal migration is observed when the oscillation period of the imposed shear is of the order of the relaxation time of the elastic membrane; hence, the optimal capillary number scales with the inverse of the oscillation frequency and the ratio agrees well with the theoretical prediction in the limit of high-frequency oscillation. The migration velocity decreases monotonically with the frequency of the applied shear and the capsule-wall distance. We report a significant correlation between the capsule lateral migration and the normal stress difference induced in the flow. The periodic variation of the capsule deformation is roughly in phase with that of the migration velocity and normal stress difference, with twice the frequency of the imposed shear. The maximum deformation increases linearly with the membrane elasticity before reaching a plateau at higher capillary numbers when the deformation is limited by the time over which shear is applied in the same direction and not by the membrane deformability. The maximum membrane deformation scales as the distance to the wall to the power 1/3 as observed for capsules and droplets in near-wall steady shear flows.

  • 126532.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Rorai, Cecilia
    Mitra, Dhrubaditya
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A microfluidic device to sort capsules by deformabilityManuscript (preprint) (Other academic)
  • 126533.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Laboratory of Fluid Mechanics and Instabilities, Switzerland .
    Rorai, Cecilia
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    A microfluidic device to sort capsules by deformability: a numerical study2014In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 10, no 39, p. 7705-7711Article in journal (Refereed)
    Abstract [en]

    Guided by extensive numerical simulations, we propose a microfluidic device that can sort elastic capsules by their deformability. The device consists of a duct embedded with a semi-cylindrical obstacle, and a diffuser which further enhances the sorting capability. We demonstrate that the device can operate reasonably well under changes in the initial position of the capsule. The efficiency of the device remains essentially unaltered under small changes of the obstacle shape (from semi-circular to semi-elliptic cross-section). Confinement along the direction perpendicular to the plane of the device increases its efficiency. This work is the first numerical study of cell sorting by a realistic microfluidic device.

  • 126534.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. Princeton Univ, Dept Mech & Aerosp Engn, Princeton, NJ 08544 USA.
    Stone, Howard A.
    Princeton Univ, Dept Mech & Aerosp Engn, Princeton, NJ 08544 USA..
    Propulsion driven by self-oscillation via an electrohydrodynamic instability2019In: Physical Review Fluids, ISSN 2469-990X, Vol. 4, no 6, article id 061701Article in journal (Refereed)
    Abstract [en]

    Oscillations of flagella and cilia play an important role in biology, which motivates the idea of functional mimicry as part of bioinspired applications. Nevertheless, it still remains challenging to drive their artificial counterparts to oscillate via a steady, homogeneous stimulus. Combining theory and simulations, we demonstrate a strategy to achieve this goal by using an elastoelectrohydrodynamic instability (based on the Quincke rotation instability). In particular, we show that applying a uniform dc electric field can produce self-oscillatory motion of a microrobot composed of a dielectric particle and an elastic filament. Upon tuning the electric field and filament elasticity, the microrobot exhibits three distinct behaviors: a stationary state, undulatory swimming, and steady spinning, where the swimming behavior stems from an instability emerging through a Hopf bifurcation. Our results imply the feasibility of engineering self-oscillations by leveraging the elastoviscous response to control the type of bifurcation and the form of instability. We anticipate that our strategy will be useful in a broad range of applications imitating self-oscillatory natural phenomena and biological processes.

  • 126535.
    Zhu, Lailai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Stone, Howard A.
    Princeton Univ, Dept Mech & Aerosp Engn, Princeton, NJ 08544 USA..
    Rotation of a low-Reynolds-number watermill: theory and simulations2018In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 849, p. 57-75Article in journal (Refereed)
    Abstract [en]

    Recent experiments have demonstrated that small-scale rotary devices installed in a microfluidic channel can be driven passively by the underlying flow alone without resorting to conventionally applied magnetic or electric fields. In this work, we conduct a theoretical and numerical study on such a flow-driven 'watermill' at low Reynolds number, focusing on its hydrodynamic features. We model the watermill by a collection of equally spaced rigid rods. Based on the classical resistive force (RF) theory and direct numerical simulations, we compute the watermill's instantaneous rotational velocity as a function of its rod number N, position and orientation. When N >= 4, the RF theory predicts that the watermill's rotational velocity is independent of N and its orientation, implying the full rotational symmetry (of infinite order), even though the geometrical configuration exhibits a lower-fold rotational symmetry; the numerical solutions including hydrodynamic interactions show a weak dependence on N and the orientation. In addition, we adopt a dynamical system approach to identify the equilibrium positions of the watermill and analyse their stability. We further compare the theoretically and numerically derived rotational velocities, which agree with each other in general, while considerable discrepancy arises in certain configurations owing to the hydrodynamic interactions neglected by the RP theory. We confirm this conclusion by employing the RP-based asymptotic framework incorporating hydrodynamic interactions for a simpler watermill consisting of two or three rods and we show that accounting for hydrodynamic interactions can significantly enhance the accuracy of the theoretical predictions.

  • 126536.
    Zhu, Lei
    KTH, School of Information and Communication Technology (ICT).
    Security Extensions of the OpenStack Platform2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The emergence of Cloud Computing has become one of hottest topics in IT industry. So, what is cloud computing? There are many definitions summarized by people from different areas in their perspectives. However, the US National Institute of Standard Technology (NIST) [1] defines cloud computing as a model for enabling ubiquitous, convenient, ondemand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) [2].

    Despite of all the benefits that Cloud Computing brings to the IT industry, there are increasing issues being pointed out about the security and privacy due to the currently immature cloud security status. NIST points out that there are several security and privacy issues in the area of public cloud computing including governance, authentication, access control, data protection and availability [3].

    This master thesis is intended to build security architecture for open-source cloud computing platform. This thesis work concentrates on providing strong authentication service between cloud provider and users, as well as delivering access control and Single- Sign-On (SSO) service to the users, which are provided by the central security system. The central security system, as the proposed solution for secure cloud-computing platform, comprises of different security components providing security services in the form of web services. OpenStack as an open-source cloud-computing platform is chose for the research.

  • 126537. Zhu, Liang-Liang
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ji, Feng-Yuan
    Ma, Xiang
    Wang, Qiao-Chun
    Tian, He
    Photolockable Ratiometric Viscosity Sensitivity of Cyclodextrin Polypseudorotaxane with Light-Active Rotor Graft2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 6, p. 3482-3486Article in journal (Refereed)
    Abstract [en]

    A prototype, based on light-active fluorescent rotor grafted to beta-cyclodextrin, shows a good solvent viscosity-sensitive behavior due to the environment-dependent nonradiative decay. With the reversible photoisomerization of the cyanostilbene unit, the viscosity sensitivity of the molecular rotor could be locked and activated, and the two switchable states can be distinguished by fluorescent signals. This cyclodextrin derivative was threaded to form a novel polypseudorotaxane. Such supramolecular assembly displays a lockable ratiometric fluorescent viscosity sensitivity with two emission channels: one aroused by fluorophore's intramolecular excimer without influenced by viscosity is used to gauge the concentration of the compound, while the other corresponding to the monomer's rotor fluorescence acts as a viscosity-sensitive signal and it can be shut off by UV irradiation.

  • 126538. Zhu, Liangliang
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sanders, Samuel N.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Unimolecular Photopolymerization of High-Emissive Materials on Cylindrical Self-Assemblies2015In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 48, no 15, p. 5099-5105Article in journal (Refereed)
    Abstract [en]

    We report a novel self-assembly pathway from a bis(imidazolyl) diphenyl-diacetylene (DPDA) compound as a realization of self-templated photopolymerization with high polymerization degrees. The work takes advantage of a cylindrical self-assembly that strengthens the preorganization of the diphenyl-diacetylene moiety at the single molecular level. On this basis, photopolymerization of DPDA can be conducted smoothly to form high-molecular-weight polydiphenyl diacetylene. Such a cylindrical self-assembly is highly dependent on molecular structure, and control studies show that only oligomers can be formed on random self-assemblies from a monoimidazolyl or nonimidazolyl diphenyl-diacetylene compound. Moreover, the cylindrical self-assembly based systems bear aggregation-induced emission enhancement characteristics and are solution processable. The leading thin-film could afford a selectively tunable function in luminescent micropatterns.

  • 126539. Zhu, Liangliang
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wu, Shaojue
    Nguyen, Kim Truc
    Yan, Hong
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhao, Yanli
    Chirality Control for in Situ Preparation of Gold Nanoparticle Superstructures Directed by a Coordinatable Organogelator2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 24, p. 9174-9180Article in journal (Refereed)
    Abstract [en]

    Imposing chirality into nanoscale superstructures is a major step forward toward systematic understanding and utilization of nanomaterials. In an attempt to achieve tunable chirality during in situ preparation of hybrid nanomaterials, we here report a novel unimolecular strategy of employing a coordinatable organogelator for the realization of chirality control in the formation of gold nanoparticle superstructures. The work takes advantage of thermally reversible sol-gel transition of the chiral dispersion as template, which causes different micelle properties that can influence the coordination ability between the organogelator and Au(III) ions. Followed by a reduction reaction, gold nanoparticle superstructures with P-helicity were prepared from the sol form of the template through a coordination-induced chiral inversion, whereas those with M-helicity were obtained from the gel form with chiral holding. Such superstructures are solvent-stable and the chirality difference between them could be observed in many solvent environments.

  • 126540. Zhu, Liangliang
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhang, Quan
    Ma, Xing
    Li, Menghuan
    Zhang, Huacheng
    Luo, Zhong
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhao, Yanli
    Unimolecular Photoconversion of Multicolor Luminescence on Hierarchical Self-Assemblies2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 13, p. 5175-5182Article in journal (Refereed)
    Abstract [en]

    Facile tuning of photophysical properties is highly desirable for boosting the performance and versatility of photoluminescent materials. In an attempt to overcome the challenge of achieving the photoswitching of multicolor luminescence on unimolecular platforms, we here report a novel hierarchical self-assembly of a cyanostilbene-naphthalimide dyad as the realization of phototunable luminescence at the unimolecular level. The work takes advantage of the photoisomerization of the cyanostilbene moiety from the Z form to its E form, which causes a morphological disorder in the molecular self-assembly and gives rise to a dual fluorescent characteristic accompanied by a progressive luminescent color conversion from yellow to green and finally to blue. Such systems with convertible multicolor luminescence might exhibit application potentials for unimolecular selective imaging and labeling, as exemplified by the cell imaging studies presented in this work.

  • 126541. Zhu, Liangliang
    et al.
    Tran, Helen
    Beyer, Frederick L.
    Walck, Scott D.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Killops, Kato L.
    Campos, Luis M.
    Engineering Topochemical Polymerizations Using Block Copolymer Templates2014In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 38, p. 13381-13387Article in journal (Refereed)
    Abstract [en]

    With the aim to achieve rapid and efficient topochemical polymerizations in the solid state, via solution-based processing of thin films, we report the integration of a diphenyldiacetylene monomer and a poly(styrene-b-acrylic acid) block copolymer template for the generation of supramolecular architectural photopolymerizable materials. This strategy takes advantage of non-covalent interactions to template a topochemical photopolymerization that yields a polydiphenyldiacetylene (PDPDA) derivative. In thin films, it was found that hierarchical self-assembly of the diacetylene monomers by microphase segregation of the block copolymer template enhances the topochemical photopolymerization, which is complete within a 20 s exposure to UV light. Moreover, UV-active cross-linkable groups were incorporated within the block copolymer template to create micropattems of PDPDA by photolithography, in the same step as the polymerization reaction. The materials design and processing may find potential uses in the microfabrication of sensors and other important areas that benefit from solution-based processing of flexible conjugated materials.

  • 126542.
    Zhu, Lin
    KTH, School of Information and Communication Technology (ICT).
    DESIGN AND IMPLEMENTATION A BATTERY MANAGEMENT SYSTEM FOR A MULTI‐FUNCTION POWER CONVERTER2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis work designed and implemented an advanced Battery Management System (BMS) for a battery package with 96 Lithium-ion battery cells connected in series. The focus of this thesis placed on battery model building, battery balancing algorithm developing, State-of-Charge (SOC) estimation algorithm developing, and implementing software in microprocessor.A set of simulation program is developed to verify the battery model and the algorithms. A battery simulator based on SPICE is built to implement a first order Thevenin dynamic electrochemical model. PID control algorithm is employed in balancing the battery cells. Meanwhile, Extended Kalman Filter (EKF) algorithm is used for estimating the SOC. An interactive web GUI application is also developed for easy control. Software running on STM32F103 microprocessor has been developed to adapt the existing BMS hardware.The simulation result proves that the first order Thevenin dynamic electrochemical model reflect the behavior of a real battery accurately, the PID balancing algorithm is effective to make the battery cells stay in balanced state and the error of EKF SOC estimation algorithm is below 5%.

  • 126543.
    Zhu, Lin
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Structural studies of HDL and applications of EM on membrane proteins2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A large number of proteins interact with biological membranes, either integrated in the membrane (PepTSo2), embedded on a membrane surface (5-lipoxygenase) or encircling a cutout of lipid bilayer (apolipoprotein1 (apoA-I). They function as transporters, receptors or biocatalysts in cellular processes like inflammation or cholesterol transport which are touched upon here. Malfunction of specific membrane proteins are the cause for several diseases or disorders.

    Knowledge of protein structure supports understanding of its mechanism of function. Here, transmission electron microscopy (TEM) was used for structure determination. To obtain structure information to high resolution for membrane proteins, normally surrounded by lipids, demands specific methods and materials for stabilization. Stabilized in detergent the structure of the bacterial transporter PepTSo2 was shown to form a tetramer even bound to substrate. However, with a protein based stabilizer, Salipro, the structure of PepTSo2 could be determined to high resolution.

    High density lipoprotein (HDL) in blood plasma, involved in the removal of cholesterol from peripheral tissues, have a central role in cardiovascular function, metabolic syndrome and diabetes.

    The HDL-particle is composed of two copies of ApoA1 and around hundred lipid molecules. From TEM data, for the first time the clearly discoidal shape could be shown by 3-dimendional reconstructions. These were used for modelling the ApoA1 protein dimer by a "biased fitting" procedure. The results indicate how ApoA1 folds around a lipid bilayer in a disc-shaped structure.

    Modified HDL called nanodiscs were here used to show the Ca2+ dependent binding of 5-lipoxygenase on the nanodisc bilayer and thereby increased production of the inflammatory mediator leukotrieneA4. Dimerization of 5-lipoxygenase inactivates these functions.

  • 126544.
    Zhu, Lin
    KTH, School of Technology and Health (STH), Basic Science and Biomedicine, Structural Biotechnology.
    Structural Studies of High Density Lipoprotein by Electron Microscopy and Flexible FittingManuscript (preprint) (Other academic)
  • 126545.
    Zhu, Lin
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Structural Biotechnology. Karolinska Institutet, Sweden.
    Petrlova, J.
    Gysbers, P.
    Hebert, Hans
    KTH, School of Technology and Health (STH), Medical Engineering, Structural Biotechnology. Karolinska Institutet, Sweden.
    Wallin, S.
    Jegerschöld, Caroline
    KTH, School of Technology and Health (STH). Karolinska Institutet, Sweden.
    Lagerstedt, J. O.
    Structures of apolipoprotein A-I in high density lipoprotein generated by electron microscopy and biased simulations2017In: Biochimica et Biophysica Acta - General Subjects, ISSN 0304-4165, E-ISSN 1872-8006, Vol. 1861, no 11, p. 2726-2738Article in journal (Refereed)
    Abstract [en]

    Background: Apolipoprotein A-I (apoA-I) in high-density lipoprotein (HDL) is a key protein for the transport of cholesterol from the vascular wall to the liver. The formation and structure of nascent HDL, composed of apoA-I and phospholipids, is critical to this process. Methods: The HDL was assembled in vitro from apoA-I, cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at a 1:4:50 molar ratio. The structure of HDL was investigated in vitreous samples, frozen at cryogenic temperatures, as well as in negatively stained samples by transmission electron microscopy. Low resolution electron density maps were next used as restraints in biased Monte Carlo simulations of apolipoprotein A-I dimers, with an initial structure derived from atomic resolution X-ray structures. Results: Two final apoA-I structure models for the full-length structure of apoA-I dimer in the lipid bound conformation were generated, showing a nearly circular, flat particle with an uneven particle thickness. Conclusions: The generated structures provide evidence for the discoidal, antiparallel arrangement of apoA-I in nascent HDL, and propose two preferred conformations of the flexible N-termini.

  • 126546. Zhu, M. -M
    et al.
    Zhao, P. -H
    Chen, Y. -L
    Bai, X. -S
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    The vorticity field of acoustic modulated free jets2012In: Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics, ISSN 0253-231X, Vol. 33, no 10, p. 1811-1814Article in journal (Refereed)
    Abstract [en]

    The motivation of this paper is to investigate the effects of acoustic modulation on the structures of free jet. Large eddy simulation is performed on three dimensional free jet of Re number 2200 with multigrid method. Comparisons of the vorticity fields are made between the unmodulated jet and perturbed jets with different modulation frequencies. When the modulation frequency is near the preferred mode of the natural jet, the flow field changes significantly. The azimuthal vorticity rolls up into large vortex rings, and the jet spreads more widely. When the modulation frequency is about the twice of the preferred mode, vortex pairing happens and the subharmonic wave becomes dominant. The flow fields are almost the same as the natural jet when the modula-tion frequency is much higher than the preferred mode. The distribution of streamwise vorticity is examined for the modulated jet near the preferred mode, and agrees qualitatively with the experiments.

  • 126547. Zhu, M. Y.
    et al.
    Sichen, Du
    KTH, Superseded Departments, Materials Science and Engineering.
    Modelling study of slag foaming phenomenon2000In: Steel research, ISSN 0177-4832, Vol. 71, no 3, p. 76-82Article in journal (Refereed)
    Abstract [en]

    A one-dimensional model based on mass and momentum conservations has been developed to predict the heights of foams caused by gas injection. In the development of the model, a dimensionless number, N-foam = u(s)[(3C(d))/(4d(b)g)](1/2) has been deduced to characterise the foaming behaviour. According to the model, an increase in this dimensionless number results in an increase In foaming height. The validity of the model has been experimentally examined using silicon oils. The experiments have also shown that foamings can be classified into two types, namely one-layer foaming and two-layer foaming. The former type results in much larger height than the latter.

  • 126548. Zhu, M-Y
    et al.
    Jones, T
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Modelling study of slag foaming by chemical reactio2001In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 30, p. 51-56Article in journal (Refereed)
  • 126549.
    Zhu, Ning
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Design, Fabrication and Characterization of Planar Lightwave Circuits Based on Silicon Nanowire Platform2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Optical devices based on Planar Lightwave Circuit (PLC) technology have well been studied due to their inherited advantages from Integrated Circuits (IC), such as: small size, high reliability, mass production and potential integration with microelectronics. Among all the materials, silicon nanowire platform gains more and more interest. The large refractive index difference between core and cladding allows tremendous reduction of the component size. This thesis studies theoretically and experimentally some integrated optical devices based on silicon nanophotonic platform, including echelle grating demultiplexers and photonic crystals.

    Some of the numerical methods are introduced first. Scalar integral diffraction method is efficient for calculating the diffraction efficiency of gratings. Beam propagation method and finite-difference time-domain method are also introduced, for simulating the light propagation along the devices.

    The fabrication technology and characterization methods are described. The fabrication steps involve: plasma assisted film deposition, E-beam lithography, RIE-etching. All these steps are proceeded under cleanroom environment. The characterization is mainly based on two methods: end-fire coupling and vertical grating coupling. The grating coupler is more efficient compared with the butt-coupling between fiber and nanowires, but is worse solution for final packaging.

    Two types of components have been realized and characterized with the above technology. The echelle grating demultiplexer is one of the key components in WDM networks. A method for increasing the diffraction efficiency based on total internal reflection is applied, and a significant improvement of the diffraction efficiency of more than 3dB is achieved. A novel cross-order echelle grating-based triplexer, a bidirectional transceiver for application in the Passive Optical Networks (PON), has been designed and fabricated, which can multi/demultiplex three channels located at 1310nm, 1490nm and 1550nm. Polarization dependence issue of echelle grating demultiplexers has been studied. Two polarization compensation schemes have been proposed, which are for the first time polarization insensitive designs of echelle grating demultiplexers based on silicon nanowire platform.

    Photonic crystal devices are also addressed in the thesis. There has been little research on the photonic crystal cavity based on pillar type. A silicon pillar type photonic crystal cavity has been fabricated with the measured Q value as high as about 104, and with an extremely high sensitivity for the changing of the background material or the effective diameter of the pillars. This kind of structure has the advantage on sensing applications compared to the air-hole type structure.

  • 126550.
    Zhu, Ning
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Dai, Daoxin
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    A hybrid modeling for the theoretical analysis of reflections in a multimode-interference coupler based on silicon-on-insulator nanowires2008In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 281, no 11, p. 3099-3104Article in journal (Refereed)
    Abstract [en]

    A hybrid method combining the three-dimensional (3D) beam propagation method (BPM) and a 3D finite-difference time-domain (FDTD) method is presented for the simulation of multimode-interference (MMI) couplers based on silicon-on-insulator (SOI) nanowires. This hybrid method makes it possible to have a robust analysis for the reflection properties while avoiding a time-consumed computation with a simplex 3D-FDTD simulation. The reflected power is sensitive to both the length and the width of the MMI coupler and thus one should choose the optimal values for good self-imaging. Furthermore, the reflection could be reduced by introducing tapers between the MMI section and the access waveguides.

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