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departmentresearch group programmeprojectcoordinates)uuid:9848d77da98a45c58077aa3735d53f04Dhttp://resolver.tudelft.nl/uuid:9848d77da98a45c58077aa3735d53f04tProduction and immobilization of lipase PCL and its application in synthesis of linolenic acid rich diacylglycerol
Liu, Nan (South China University of Technology); Liu, D. (South China University of Technology); Wang, Weifei (Guangdong Academy of Agricultural Sciences); Hollmann, F. (TU Delft BT/Biocatalysis); Xu, Long (South China University of Technology); Ma, Yunjian (South China University of Technology); Yang, Bo (South China University of Technology); Bai, Weidong (Zhongkai University of Agriculture and Engineering); Sun, Xiaotao (Beijing Technology and Business University); Wang, Yonghua (South China University of Technology) Linolenic acid rich diacylglycerol has been demonstrated with promising health promotion functions. This study examined the production, immobilization of lipase PCL, and its application in the synthesis of diacylglycerol by esterification of linolenic acid with glycerol. The resin ECR8806 was selected as an effective support for the immobilization of lipase PCL. Fourier transform infrared and Laser scanning confocal microscope analysis proved that the lipase was successfully immobilized on the resin. Compared with the free PCL, the immobilized one exhibited higher temperature tolerance. Under optimized reaction conditions, a DAG content of 54.49% were obtained. After further purified by molecular distillation, the purity of DAG was up to 99.28%. During esterification, the immobilized PCL was quite stable and retained more than 91.60% of its initial activity after 10 cycles. These new findings on the immobilized PCL will make it to be a prospective enzyme in oils and fats industry.Mdiacylglycerol; esterification; immobilization; reusability; aLinolenic acidenjournal article`Accepted Author Manuscript Green Open Access added to TU Delft Institutional Repository You share, we take care! Taverne project https://www.openaccess.nl/en/yousharewetakecare Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.
20190123BT/Biocatalysis)uuid:fa60af40f2b743b1853cb13a083aca32Dhttp://resolver.tudelft.nl/uuid:fa60af40f2b743b1853cb13a083aca32Modelling of deformation and fracture for a model quasibrittle material with controlled porosity: Synthetic versus real microstructure`avija, B. (TU Delft Materials and Environment); Smith, G.E. (University of Bristol); Liu, D (University of Bristol; University of Oxford); Schlangen, H.E.J.G. (TU Delft Materials and Environment); Flewitt, P.E.J. (University of Bristol)Deformation and fracture of materials are usually considered in terms of brittle and ductile modes. However, there is an intermediate class between these limits that is termed quasibrittle where there is measurable inelastic deformation prior to final graceful brittle failure. In previous work, we presented deformation and fracture data obtained tests conducted using a model material containing different known amounts of up to about 30% surrogate porosity. The model material is a hemihydrate gypsum plaster with additions of expanded polystyrene beads in the size range 1.5 2.0/ mm dia. Use of gypsum plaster and artificial pores enabled creating a simple brittle model material with isolated pores randomly distributed and their size and geometry controlled. Herein, a comparison between two ways of generating microstructures for computer modelling of deformation and fracture of the model material is presented. The predictions for the computer model have been based upon two microstructure inputs (i) a synthetic 3D pore model and (ii) measurements of porosity obtained from computed Xra< y tomography images of the test material. Predictions of the elastic modulus and tensile strength for the different amount of porosity are compared between the two computer models and the experimental flexural data. The predicted deformation and fracture characteristics that describe the observed quasi brittle response measured for the model material are discussed.EGreen Open Access added to TU Delft Institutional Repository You share, we take care! Taverne project https://www.openaccess.nl/en/yousharewetakecare Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.
20190506Materials and Environment)uuid:bbfcab2fe30b41caa95c4a14df97ede6Dhttp://resolver.tudelft.nl/uuid:bbfcab2fe30b41caa95c4a14df97ede6AProtruding organic surfaces triggered by inplane electric fieldsLiu, D. (TU Delft ChemE/Organic Materials and Interfaces; South China Normal University); Tito, Nicholas B. (Eindhoven University of Technology); Broer, Dirk J. (Eindhoven University of Technology)Coatings with a dynamic surface topography are of interest for applications in haptics, soft robotics, cell growth in biology, hydro and air dynamics and tribology. Here we propose a design for creating oscillating surface topographies in thin liquid crystal polymer network coatings under an electric field. By applying an alternating electric field, the coating surface deforms, and predesigned local corrugations appear. The continuous AC electric field further initiates oscillations superimposed on the formed topographies. This effect is based on microscopic free volume creation. By exciting the liquid crystal network at its resonance frequency, maximum free volume is generated and large surface topographies are formed. Molecular simulation is used to examine this behaviour in microscopic detail as a function of oscillation frequency. Surface topography formation is fast and reversible. Excess free volume is energetically unfavourable, thus the surface topographies disappear within seconds once the electric field is removed.&ChemE/Organic Materials and Interfaces)uuid:074d4f96e7bf4ddea7b486c9dd2e214fDhttp://resolver.tudelft.nl/uuid:074d4f96e7bf4ddea7b486c9dd2e214f]Increasing the Feasibility of Superconducting Generators for 10 MW DirectDrive Wind Turbines:Liu, D. (TU Delft DC systems, Energy conversion & Storage)Ferreira, J.A. (promotor); Polinder, H. (copromotor); Abrahamsen, Asger Bech (copromotor); Delft University of Technology (degree granting institution)In recent years, superconducting synchronous generators (SCSGs) have been proposed as an alternative to permanent magnet synchronous generators (PMSGs). They are expected to reduce the top head mass and the nacelle size for such large wind turbines. In 2012, the INNWIND.EU project initiated this research to investigate SCSGs for 1020MWdirectdrive offshore wind turbines. However, the feasibility of SCSGs was limited by a few critical issues, such as high costs, AC losses in the superconducting winding and excessive short circuit torque. Furthermore, SCSG designs proposed in the literature were various but all less competitive than PMSGs.BFeasibility; superconducting generator; directdrive; wind turbinedoctoral thesis9789462996274'DC systems, Energy conversion & Storage)uuid:adc422cd2dfc4f18b288c7be4a5bcbf5Dhttp://resolver.tudelft.nl/uuid:adc422cd2dfc4f18b288c7be4a5bcbf5VPotential of Partially Superconducting Generators for Large DirectDrive Wind TurbinesLiu, D. (TU Delft DC systems, Energy conversion & Storage); Polinder, H. (TU Delft DC systems, Energy conversion & Storage); Abrahamsen, Asger B. (Technical University of Denmark); Ferreira, J.A. (TU Delft ESE Programmes)cThis paper aims at assessing the potential of partially superconducting generators for 10 MW directdrive wind turbines by investigating their performance for a very wide range of excitation currents. Performance indicators such as shear stress and efficiency and other generator charac< teristics are compared for 12 different generator topologies. To be sufficiently attractive, superconducting generators must have significant advantages over permanent magnet directdrive generators, which typically have shear stresses of the order of 53 kPa and efficiencies of 96%. Therefore, we investigate what excitation is required to obtain a doubled shear stress and an efficiency of 98%. To achieve this, the different topologies require a range of excitation from 200 to 550 kAt (ampereturns) with a low armature current density of 2 A/mm2. The more iron that is used in the core of these topologies, the easier they achieve this performance. By examining the maximum magnetic flux density at the location of the superconducting field winding, feasible superconductors can be chosen according to their engineering current density capabilities. It is found that high and lowtemperature superconductors can meet the performance criteria for many of the topologies. MgB2 superconductors are feasible for the fully ironcored topology with salient poles but need cooling down to 10 K.YDirect drive; high temperature superconductor (HTS); low temperature superconductor (LTS)Accepted Author Manuscript)uuid:93ac17aba7274f0fbe496ee1c40ee168Dhttp://resolver.tudelft.nl/uuid:93ac17aba7274f0fbe496ee1c40ee168Towards understanding the influence of porosity on mechanical and fracture behaviour of quasibrittle materials: Experiments and modellingLiu, D (University of Bristol; University of Oxford); `avija, B. (TU Delft Materials and Environment); Smith, G.E. (University of Bristol); Flewitt, P.E.J. (University of Bristol); Lowe, T.; Schlangen, H.E.J.G. (TU Delft Materials and Environment)In this work, porosityproperty relationships of quasibrittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (CaSO 4 "1/2H 2 O CaSO4"1/2H2O) and expanded spherical polystyrene beads (1.5 2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D Xray computed tomography. Beams of the size of 2020150 2020150 mm were cast and loaded under fourpoint bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a latticebased multiscale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasibrittle materials.;Quasibrittle materials; Porosity; Strength; Microstructure)uuid:e147390075ba402f9f1919ddd7dc2b82Dhttp://resolver.tudelft.nl/uuid:e147390075ba402f9f1919ddd7dc2b82QShort Circuits of a 10 MW High Temperature Superconducting Wind Turbine GeneratorDSong, X. (Technical University of Denmark); Liu, D. (TU Delft DC systems, Energy conversion & Storage); Polinder, H. (TU Delft DC systems, Energy conversion & Storage); Mijatovic, Nenad (Technical University of Denmark); Holbll, Joachim (Technical University of Denmark); Jensen, Bogi Bech (University of the Faroe Islands)Direct drive high temperature superconducting (HTS) wind turbine generators have been proposed to tackle challenges for ever increasing wind turbine ratings. Due to smaller reactances in HTS generators, higher fault currents and larger transient torques cou< ld occur if sudden short circuits happen at generator terminals. In this paper, a finite element model that couples magnetic fields and the generator s equivalent circuits is developed to simulate short circuit faults. Afterwards, the model is used to study the transient performance of a 10 MW HTS wind turbine generator under four different short circuits, i.e., threephase, phasephase clear of earth, phasephaseearth, and phaseearth. The stator current, fault torque, and field current under each short circuit scenario are examined. Also included are the forces experienced by the HTS field winding under short circuits. The results show that the short circuits pose great challenges to the generator, and careful consideration should be given to protect the generator. The findings presented in this paper would be beneficial to the design, operation and protection of an HTS wind turbine generator.dFinite element analysis; force; high temperature superconducting generator; short circuit; transient)uuid:40e6a41f757e4960be477d4bdb179804Dhttp://resolver.tudelft.nl/uuid:40e6a41f757e4960be477d4bdb179804KComparison of NestedLoop Rotors in Brushless DoublyFed Induction MachinesWang, X. (TU Delft DC systems, Energy conversion & Storage); Liu, D. (TU Delft DC systems, Energy conversion & Storage); Lahaye, D.J.P. (TU Delft Numerical Analysis); Polinder, H. (TU Delft DC systems, Energy conversion & Storage); Ferreira, J.A. (TU Delft Electrical Power Processing)The brushless doublyfed induction machine (DFIM) has great potential as a variablespeed generator for wind turbine applications. This special machine has a richer spaceharmonic spectrum due to its special nestedloop rotor construction compared with conventional induction machines. It may result in higher iron losses, higher torque ripple and more timeharmonics adding to the grid total harmonic distortion (THD). This paper applies the 2D finite element (FE) model to investigate several different nested loop rotor constructions. It shows the outer loop makes more contribution to the torque while the inner loop plays a small role in the torque production. The most outer loop determines the overall THD level while the inner one has little influence on it. The THD could be reduced by increasing the number of the outer loops. More machine performances could be studied to derive more guidelines for designing the<br/>middle loops.\permanent magnet machine; Concentrated winding; eddy current losses; experimental validationconference paperIEEE)uuid:bbae3221ebdb4a348dec7f89546b2f22Dhttp://resolver.tudelft.nl/uuid:bbae3221ebdb4a348dec7f89546b2f22aGoogleEarth Based Visualizations for Environmental Flows and Pollutant Dispersion in Urban AreasLiu, D. (Shanghai Advanced Research Institute; University of Chinese Academy of Science); Kenjeres, S. (TU Delft ChemE/Transport Phenomena)4In the present study, we address the development and application of an efficient tool for conversion of results obtained by an integrated computational fluid dynamics (CFD) and computational reaction dynamics (CRD) approach and their visualization in the Google Earth. We focus on results typical for environmental fluid mechanics studies at a city scale that include characteristic wind flow patterns and dispersion of reactive scalars. This is achieved by developing a code based on the Java language, which converts the typical fourdimensional structure (spatial and temporal dependency) of data results in the Keyhole Markup Language (KML) format. The visualization techniques most often used are revisited and implemented into the conversion tool. The potential of the tool is demonstrated in a case study of smog formation due to an intense traffic emission in Rotterdam (The Netherlands). It is shown that the Google Earth can provide a computationally efficient and userfriendly means of data representation. This feature can be very useful for visualization of pollution at street levels, which is of great importance for the city residents. Various meteorological and traffic emissions can be easily vi< sualized and analyzed, providing a powerful, userfriendly tool for traffic regulations and urban climate adaptations.Wcomputational fluid dynamics; visualization; Google Earth; environmental pollution; KMLChemE/Transport Phenomena)uuid:c9c93b5e64aa4889b5b3ebe012e2b8f1Dhttp://resolver.tudelft.nl/uuid:c9c93b5e64aa4889b5b3ebe012e2b8f1Comparison of Levelized Cost of Energy of a 10 MW superconducting and magnetic pseudo direct drive generator targeted for the INNWIND.EU reference turbinexAbrahamsen, Asger Bech (Technical University of Denmark); Liu, D. (TU Delft DC systems, Energy conversion & Storage); Magnusson, Niklas (SINTEF); Thomas, A (Siemens Wind Power); Z., Azar (Siemens Wind Power); Stehouwer, Ewoud (DNVGL); Hendriks, E (Knowledge Centre WMC); Penzkofer, A. (University of Sheffield); Atallah, K (University of Sheffield); Dragan, R.R. (Magnomatics); .Clark, R.E. (Magnomatics); Deng, F. (Aalborg University); Chen, Z (Aalborg University); Karwatzki, D. (Leibniz Universitt); Mertens, A. (Leibniz Universitt); Parker, M. (University of Strathclyde); Finney, SJ (University of Strathclyde); Polinder, H.Innovative drive trains targeted at 1020 MW offshore turbines are investigated in the INNWIND.EU project in order to determine the impact on the Levelized Cost of Energy (LCoE) resulting when installed in the ,North sea at 50 m of water [1]. The two main technologies studied are superconducting direct drive (SCDD)[2] and the magnetic pseudo direct drive (PDD) [3] generators, which are both capable to providing compact drive trains with low weight and a small number of moving parts compared to a gearbox based drive train (see figure 1a). Superconducting field coils are used to provide the torque in the direct drive generators, where the armature windings are based on conventional copper wire and magnetic steel laminates operated at ambient temperature. Magnetic pseudo direct drive generators consist of a magnetic gearbox made of an inner free rotor (rotating at a geared up speed to the blade input) and an intermediate drive rotor inserted into an outer static armature winding, where the electricity is harvested.)uuid:624e0a6f854f463bbe4c62af81f363adDhttp://resolver.tudelft.nl/uuid:624e0a6f854f463bbe4c62af81f363adFinite Element Analysis and Experimental Validation of Eddy Current Losses in Permanent Magnet Machines with FractionalSlot Concentrated WindingsgPermanentmagnet machines with fractional slot concentrated windings are easy to manufacture. Their popularity therefore is steadily increasing. Without a proper design, however, the induced eddycurrent losses in the solid rotor get rather high. The modeling and the prediction of eddycurrent losses for these machines are thus very important during the design process. This paper focuses on the finiteelement analysis and the experimental validation of eddycurrent losses for this kind of machine with a small axial length. Twodimensional and threedimensional transient finiteelement models are developed for computing the eddycurrent losses. The rotor motion is taken into account using an Arbitrary LagrangianEulerian formulation. The total iron losses are measured experimentally and a method to separate the rotor iron losses from the total iron losses is presented. The validation results show that the twodimensional finiteelement model overestimates the losses due to the endeffects being neglected. The threedimensional model agrees much better with the measurements in both noload and onload operations.\Concentrated winding; eddy current losses; experimental validation; permanent magnet machine)uuid:98088329676a4ba0b76e4dfb48e4eb4eDhttp://resolver.tudelft.nl/uuid:98088329676a4ba0b76e4dfb48e4eb4eDSong, X. (Technical University of Denmark); Polinder, H. (TU Delft DC systems, Energy conversion & Storage); Liu, D. (TU Delft DC systems, Energy conversion & Storage); Mijatovic, Nenad (Technical University of Denmark); Holbll, Joachim (Technical University of Denmark); Jensen, Bogi Bech (University of the Faroe Islands)Direct drive high temperatur< e superconducting (HTS) wind turbine generators have been proposed to tackle challenges for ever increasing wind turbine ratings. Due to smaller reactances in HTS generators, higher fault currents and larger transient torques could occur if sudden short circuits happen at generator terminals. In this paper, a finite element model that couples magnetic fields and the generator s equivalent circuits is developed to simulate short circuit faults. Afterwards, the model is used to study the transient performance of a 10 MW HTS wind turbine generator under four different short circuits, i.e., threephase, phasephase clear of earth, phasephaseearth, and phaseearth. The stator current, fault torque, and field current under each short circuit scenario are examined. Also included are the forces experienced by the field winding under short circuits. The results show that the short circuits pose great challenges to the generator, and careful consideration should be given to protect the generator. The results presented in this paper would be beneficial to the design, operation and protection of an HTS wind turbine generator.dFinite element analysis; Force; High temperature superconducting generator; Short circuit; Transient)uuid:942520af74694fff889340e007f52496Dhttp://resolver.tudelft.nl/uuid:942520af74694fff889340e007f52496zAn experimental and modelling evaluation of the deformation and fracture of quasibrittle reticulated vitreous carbon foamHeard, P; `avija, B. (TU Delft Materials and Environment); Liu, D; Smith, GE; Hallam, KR; Schlangen, H.E.J.G. (TU Delft Materials and Environment); Flewitt, P.E.J.Gdoutos, Emmanuel E. (editor)In quasibrittle materials the addition of specific microstructural features such as porosity can lead to departure from linear elastic behaviour prior to maximum force, followed by graceful failure. A simple but extreme example is reticulated vitreous carbon foam, with its opencell structure of brittle ligaments connected in a threedimensional array. Tensile testing has been made on foams with various pore and ligament dimensions to provide a measure of forcedisplacement, combined with acoustic monitoring, and evaluation of the associated elastic moduli and fracture strengths. These tests provide insights into the mechanisms of quasibrittle failure. The results are explored by comparing with predictions from a microstructurebased finite beam element model. Inputs to the model are the elastic modulus and fracture strength of the individual ligaments of the foam measured at the micro lengthscale. Results are discussed with respect to the energy of fracture, the distribution and progression of fracture for individual ligaments.)uuid:157577233ac74188a4894218436e2aa0Dhttp://resolver.tudelft.nl/uuid:157577233ac74188a4894218436e2aa0^Multiscale characterization and modelling of damage evolution in nuclear Gilsocarbon graphiteELiu, D.; Heard, P.; Savija, B.; Smith, G.; Schlangen, E.; Flewitt, P..In the present work, the microstructure and mechanical properties of Gilsocarbon graphite have been characterized over a range of lengthscales. Optical imaging, combined with 3D Xray computed tomography and 3D highresolution tomography based on focus ion beam milling has been adopted for microstructural characterization. A range of smallscale mechanical testing approaches are applied including an in situ microcantilever technique based in a Dualbeam workstation. It was found that pores ranging in size from nanometers to tens of micrometers in diameter are present which modify the deformation and fracture characteristics of the material. This multiscale mechanical testing approach revealed the significant change of mechanical properties, for example flexural strength, of this graphite over the lengthscale from a micrometer to tens of centimeters. Such differences emphasize why input parameters to numerical models have to be undertaken at the appropriate lengthscale to allow predictions of the deformation, fracture and the stochastic features of the strength of the graphite with the required confidence< . Finally, the results from a multiscale model demonstrated that these data derived from the microscale tests can be extrapolated, with high confidence, to large components with realistic dimensions.xray tomography; fracture; nuclear materialsMaterials Research Society!Civil Engineering and GeosciencesStructural Engineering)uuid:aabe6d90068141399a6d201e70843eadDhttp://resolver.tudelft.nl/uuid:aabe6d90068141399a6d201e70843ead1ILIGRA: An Efficient Inverse Line Graph Algorithm)Liu, D.; Trajanovski, S.; Van Mieghem, P.#This paper presents a new and efficient algorithm, ILIGRA, for inverse line graph construction. Given a line graph H, ILIGRA constructs its root graph G with the time complexity being linear in the number of nodes in H. If ILIGRA does not know whether the given graph H is a line graph, it firstly assumes that H is a line graph and starts its root graph construction. During the root graph construction, ILIGRA checks whether the given graph H is a line graph and ILIGRA stops once it finds H is not a line graph. The time complexity of ILIGRA with line graph checking is linear in the number of links in the given graph H. For sparse line graphs of any size and for dense line graphs of small size, numerical results of the running time show that ILIGRA outperforms all currently available algorithms.'graph algorithm; line graph; root graphSpringer8Electrical Engineering, Mathematics and Computer Science&Network Architectures & Services (NAS))uuid:01387120a39a477faceae5b902b018faDhttp://resolver.tudelft.nl/uuid:01387120a39a477faceae5b902b018faODesign study of a 10 MW MgB2 superconductor direct drive wind turbine generatorSAbrahamsen, A.B.; Magnusson, N.; Liu, D.; Stehouwer, E.; Hendriks, B.; Polinder, H..A superconducting direct drive generator based on field windings of MgB2 superconducting tape is proposed as a solution by mounting the generator in front of the blades using a kingpin nacelle design for offshore turbines with power ratings larger than 10 MW as investigated in the INNWIND.EU project.]superconducting generator; direct drive generator; offshore wind turbine; nacelle integrationEWEAElectrical Sustainable Energy)uuid:fabc0cb6e8684bf484c2f45cfc7d6642Dhttp://resolver.tudelft.nl/uuid:fabc0cb6e8684bf484c2f45cfc7d6642IDesign of an MgB2 race track coil for a wind generator pole demonstrationDAbrahamsen, A.B.; Magnusson, N.; Jensen, B.B.; Liu, D.; Polinder, H.PAn MgB2 race track coil intended for demonstrating a down scaled pole of a 10 MW direct drive wind turbine generator has been designed. The coil consists of 10 double pancake coils stacked into a race track coil with a cross section of 84 mm x 80 mm. The length of the straight section is 0.5 m and the diameter of the end sections is 0.3 m. Expanded to a straight section of 3.1 m it will produce about 1.5 T magnetic flux density in the air gap of the 10 MW 32 pole generator and about 3.0 T at the edge of the superconducting coil with an operation current density of the coil of 70 A/mm2.IOP)uuid:421840158cac4be28084a221744d0452Dhttp://resolver.tudelft.nl/uuid:421840158cac4be28084a221744d0452\Feasibility Study of a 10 MW MgB2 Fully Superconducting Generator for Offshore Wind Turbines2Kostopoulos, D.; Liu, D.; Genani, G.; Polinder, H.Offshore wind is considered a vital component of the future large scale renewable generation portfolio. Intense R&D effort is occurring in both the technology and the supply chain aiming at cost reduction. The drivetrain of wind turbines is an area of continuous evolution with currently no one standard configuration in the industry. It is anticipated that in order to upscale offshore wind turbines in the 10+ MW power range innovation is necessary in this subsystem. A possible solution could be the adoption of superconductivity technology. The potential benefits are multiple comprising weight, dimension and cost reduction in both capital and operating costs. In this paper a rough analytical design is presented of an MgB2 fully superconducting wind turbine generator (WTG). An analytical cu< rrent sheet distribution is adopted to calculate the magnetic field of the generator and a finite element method (FEM) analysis is used to verify the field calculation. The objective of this work is to assess the technical feasibility of this generator topology and attempt to extract more general conclusions regarding the potential application of superconducting drivetrains in offshore wind turbines. European Wind Energy Association)uuid:7a2dcf0be88e4da6baa959cfc4cc63adDhttp://resolver.tudelft.nl/uuid:7a2dcf0be88e4da6baa959cfc4cc63ad\Robustness and Optimization of Complex Networks: Reconstructability, Algorithms and ModelingLiu, D.Van Mieghem, P. (promotor)EThe infrastructure networks, including the Internet, telecommunication networks, electrical power grids, transportation networks (road, railway, waterway, and airway networks), gas networks and water networks, are becoming more and more complex. The complex infrastructure networks are crucial to our human society, and it has been a hot research eld to make our complex infrastructure networks more robust and optimize the performance of them. Besides mandesigned infrastructure networks, complex networks also cover many natural networks, such as social networks, ecological networks, and biological networks. In order to tackle some of the di cult social issues, ecological problems, and unsolved medical problems, we must learn how these natural complex networks organize, operate, and function. Complex networks can be represented by graphs. A graph consists of a collection of nodes and a collection of links that connect the nodes. A graph is uniquely described by its adjacency matrix, of which the entry on row i and column j is one only if node i and node j in the graph is connected by a link, otherwise the entry is zero. Each adjacency matrix is associated to a unique set of eigenvalues and corresponding eigenvectors. The eigenvalues and corresponding eigenvectors of a graph, also called the spectrum of the graph, contains all the information of the graph, and the topological/physical meanings of some eigenvalues and eigenvectors are already known. The knowledge on the spectra of networks is of crucial importance to the many aspects of the researches on complex network, such as connectivity of networks and virus spreading in networks. The line graph l (G) of a graph G has a set of nodes mapping the set of links in G, and two nodes in l (G) are adjacent if and only if the corresponding links in G have a node in common. Some problems of graphs can be transformed to much easier ones in the domain of line graphs. For example, partitioning the nodes to nd the overlapping communities in a graph can be done by partitioning the links in the line graph of the concerned graph. Moreover, the line graphs often share common features with realworld complex networks, like highly clustered and assortative mixing. Hence, the line graphs are considered by many to model realworld complex networks. The robustness and optimization of complex network is a rather broad research field. We focus on the reconstruction of complex networks from the spectral domain and the line graph domain. This thesis is organized as follows. We first study the reconstruction of networks from their eigenvalues and eigenvectors and the spectral properties of networks. In the second part of this thesis, we present two algorithms which reconstruct networks from the line graph domain, the properties of the line graphs, and a random line graph model. We at last give the research results on two types of realworld networks. The adjacency matrix of a graph can be computed with its eigenvalues and eigenvectors. When some of the eigenvalues are set to zero, the adjacency matrix can still be correctly computed. We propose a measure, the reconstructability coefficient, defined as the maximum number of eigenvalues that can be removed. We find that the reconstructability coefficient is linear function of the size of the network for all networks that we have studied. We give some results on the spectral metric, the energy< of a graph, which is defined by the sum of the absolute value of all the eigenvalues. We also explore the relations between graph energy and the topological metric, assortativity, for many different types of networks. For the reconstruction of networks from the line graph domain, we propose two algorithms Marinlinga and Iligra. While all previous algorithms rely on Whitney's theorem, Marinlinga is based on the principle of link relabeling and endnode recognition. Iligra reconstructs the graphs from the line graph domain with the linear time complexity. This thesis extends the researches in the line graph domain. We find that the number of links in a line graph with a fixed number of nodes can not take some consecutive natural numbers, and these numbers are called a bandgap of the line graph. We present the exact expressions of the bands and bandgaps of the number of links in line graphs. In order to facilitate the researches in the line graph domain, we propose a model which randomly generates line graphs. The essence of our model is to merge step by step a pair of nodes in cliques, subjecting to some rules to ensure that the resulting graphs are line graphs. Thanks to the random line model, a method to generate a serial of graphs of which the assortativity increases linearly has been invented. This thesis studies two types of realworld networks: social networks and human brain networks. We characterize the overlapping community structure of the social networks of ArXiv coauthorship, IMDB actors collaboration and SourceForge collaboration, and propose a growing hypergraph model, based on preferential attachment. The proposed hypergraph model captures the fundamental properties including the powerlaw distributions of group size, group degree, overlapping depth, individual degree and interestsharing number of realworld affiliation networks, and reproduces the properties of high clustering, assortative mixing and short average path length of social networks. To study brain networks, we propose a spectral randomness metric to quantize the randomness of networks. Based on the randomness measuring method, we have found that the brain networks of Alzheimers disease are statistically more random than the healthy brain networks.complex networks; graph spectra; reconstructability; line graphs; social networks; community structure; hypergraphs; brain networks; randomness*Next Generation Infrastructures FoundationIntelligent Systems)uuid:fb00d9126de2401aabe70bb3a90aaf30Dhttp://resolver.tudelft.nl/uuid:fb00d9126de2401aabe70bb3a90aaf305Random line graphs and a linear law for assortativityFor a fixed number N of nodes, the number of links L in the line graph H(N,L) can only appear in consecutive intervals, called a band of L. We prove that some consecutive integers can never represent the number of links L in H(N,L), and they are called a bandgap of L. We give the exact expressions of bands and bandgaps of L. We propose a model which can randomly generate simple graphs which are line graphs of other simple graphs. The essence of our model is to merge step by step a pair of nodes in cliques, which we use to construct line graphs. Obeying necessary rules to ensure that the resulting graphs are line graphs, two nodes to be merged are randomly chosen at each step. If the cliques are all of the same size, the assortativity of the line graphs in each step are close to 0, and the assortativity of the corresponding root graphs increases linearly from ?1 to 0 with the steps of the nodal merging process. If we dope the constructing elements of the line graphs the cliques of the same size with a relatively smaller number of cliques of different size, the characteristics of the assortativity of the line graphs is completely altered. We also generate line graphs with the cliques whose sizes follow a binomial distribution. The corresponding root graphs, with binomial degree distributions, zero assortativity, and semicircle eigenvalue distributions, are equivalent to Erd?sRnyi random graphs.American Physical Society)uuid:bf9fac6a9ca849< 9fb3d51d4ce29c90b9Dhttp://resolver.tudelft.nl/uuid:bf9fac6a9ca8499fb3d51d4ce29c90b94Characterizing the Structure of Affiliation Networks'Liu, D.; Blenn, N.; Van Mieghem, P.F.A.Vur society contains all types of organizations, such as companies, research groups and hobby clubs. Affliation networks, as a large and important portion of social networks, consist of individuals and their affiation relations: Two individuals are connected by a link if they belong to the same organization(s). Affliation networks naturally contain many fully connected cliques, since the nodes of the same organization are all connected with each other by de?nition. In this paper, we present methods which facilitate the computation for characterizing the realworld affliation networks of ArXiv coauthorship, IMDB actors collaboration and SourceForge collaboration. We propose a growing hypergraph model with preferential attachment for affliation networks which reproduces the clique structure of af?liation networks. By comparing computational results of our model with measurements of the realworld affliation networks of ArXiv coauthorship, IMDB actors collaboration and SourceForge collaboration, we show that our model captures the fundamental properties including the powerlaw distributions of group size, group degree, overlapping depth, individual degree and interestsharing number of realworld affliation networks, and reproduces the properties of high clustering, assortative mixing and short average path length of realworld affliation networks.?affliation network; hypergraph; line graph; eigvalue; power lawElsevier)uuid:5878951acd724c0684070b7c0d187ef3Dhttp://resolver.tudelft.nl/uuid:5878951acd724c0684070b7c0d187ef3IA Social Network Model Exhibiting Tunable Overlapping Community StructuremSocial networks, as well as many other realworld networks, exhibit overlapping community structure. In this paper, we present formulas which facilitate the computation for characterizing the overlapping community structure of networks. A hypergraph representation of networks with overlapping community structure is introduced. Using the hypergraph representation we setup a social network model which exhibits innate tunable overlapping community structure. By comparing simulation results of our model with results of the Hyves network and the SourceForge network, we show that our model captures most of the common features of large social networks. We analytically give the relation between the maximum membership number of a network and the adjacency eigenvalues of the simple graph representation of the network, which is the line graph of the hypergraph representation.Usocial networks; overlapping community structure; preferential attachment; hypergraph)uuid:46dedfa7d6e74f2988f7a7ea0a8b87d1Dhttp://resolver.tudelft.nl/uuid:46dedfa7d6e74f2988f7a7ea0a8b87d1:Decreasing the spectral radius of a graph by link removals]Van Mieghem, P.; Stevanovi?, D.; Kuipers, F.; Li, C.; Van de Bovenkamp, R.; Liu, D.; Wang, H.XThe decrease of the spectral radius, an important characterizer of network dynamics, by removing links is investigated. The minimization of the spectral radius by removing m links is shown to be an NPcomplete problem, which suggests considering heuristic strategies. Several greedy strategies are compared, and several bounds on the decrease of the spectral radius are derived. The strategy that removes that link l=i~j with largest product (x1)i(x1)j of the components of the eigenvector x1 belonging to the largest adjacency eigenvalue is shown to be superior to other strategies in most cases. Furthermore, a scaling law where the decrease in spectral radius is inversely proportional to the number of nodes N in the graph is deduced. Another sublinear scaling law of the decrease in spectral radius versus the number m of removed links is conjectured.Telecommunications)uuid:a70dcd658114458db61a5cd8d46f54ebDhttp://resolver.tudelft.nl/uuid:a70dcd658114458db61a5cd8d46f54eb@Spectral perturbation and reconstructability of complex networks"Liu, D.; Wang<, H.; Van Mieghem, P.rIn recent years, many network perturbation techniques, such as topological perturbations and service perturbations, were employed to study and improve the robustness of complex networks. However, there is no general way to evaluate the network robustness. In this paper, we propose a global measure for a network, the reconstructability coefficient ?, defined as the maximum number of eigenvalues that can be removed, subject to the condition that the adjacency matrix can be reconstructed exactly. Our main finding is that a linear scaling law, E[?]=aN, seems universal in that it holds for all networks that we have studied.
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