"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:7b8a6244-8885-4fb5-8a10-ece47e36d8ef","http://resolver.tudelft.nl/uuid:7b8a6244-8885-4fb5-8a10-ece47e36d8ef","A Numerical Investigation of the Effects of Groove Texture on the Dynamics of a Water-Lubricated Bearing–Rotor System","Feng, H. (TU Delft Mechatronic Systems Design; Hohai University); Gao, Zhiwei (Hohai University); van Ostayen, R.A.J. (TU Delft Mechatronic Systems Design); Zhang, Xiaofeng (Hohai University)","","2023","This paper aims to investigate the combined effects of working condition and structural parameters of groove texture on the dynamic characteristics, stability and unbalance response of a water-lubricated hydrodynamic bearing–rotor system to avoid instability and excessive vibration of the rotor. The Navier–Stokes equation, standard K-ε model with enhanced wall treatment and Zwart–Gerber–Belamri cavitation model are considered using the commercial software Fluent to calculate the stiffness and damping coefficients of a groove-textured, water-lubricated bearing based on the dynamic mesh method; the critical mass to express the stability and the unbalance response solved by the fourth order Runge–Kutta method of the rotor are calculated based on dynamic equations. The results indicate that shallower and longer groove textures can improve the direct stiffness along the load direction (Formula presented.), weaken the stiffness in the orthogonal direction (Formula presented.), improve stability and decrease the unbalance response amplitude of the water-lubricated bearing–rotor system at a greater rotational speed and smaller eccentricity ratio; however, the impact of grooves on damping parameters is not as great as it is on stiffness—there exists an optimum groove width to achieve a best dynamic performance.","surface texture; water-lubricated hydrodynamic bearing; dynamic characteristics; stability; unbalance response; rigid rotor","en","journal article","","","","","","","","","","","Mechatronic Systems Design","","",""
"uuid:c47e9ed9-c91d-4007-bc37-246be675236a","http://resolver.tudelft.nl/uuid:c47e9ed9-c91d-4007-bc37-246be675236a","Lysozyme stability in various deep eutectic solvents using molecular dynamics simulations","Hebbar, Akshatha (Manipal Academy of Higher Education (MAHE)); Dey, P. (TU Delft Team Poulumi Dey); Vatti, Anoop Kishore (Manipal Academy of Higher Education (MAHE))","","2023","The ability of neat deep eutectic solvents (DESs) to influence protein structure and function has gained considerable interest due to the unstable nature of enzymes or therapeutic proteins, which are often exposed to thermal, chemical, or mechanical stresses when handled at an industrial scale. In this study, we simulated a model globular protein, lysozyme, in water and six choline chloride-based DES using molecular dynamics simulations, to investigate the structural changes in various solvent environments, giving insights into the overall stability of lysozyme. Root mean square deviation (RMSD) and root mean square fluctuations (RMSF) of the C-α backbone indicated that most DESs induced a less flexible and rigid lysozyme structure compared to water. The radius of gyration and end-to-end distance calculations pointed towards higher structural compactness in reline and levuline, while the structure of lysozyme considerably expanded in oxaline. Protein-solvent interactions were further analysed by hydrogen bonding interactions and radial distribution functions (RDF), which indicated a higher degree of lysozyme-hydrogen bond donor (HBD) interactions compared to lysozyme-choline hydrogen bonding. Surface area analysis revealed an overall % increase in total positive, negative, donor, and acceptor surface areas in malicine and oxaline compared to water and other DESs, indicating the exposure of a larger number of residues to interactions with the solvent. Reline, levuline, and polyol-based DESs comparatively stabilized lysozyme, even though changes in the secondary/tertiary structures were observed. Communicated by Ramaswamy H. Sarma.","deep eutectic solvents; Lysozyme; molecular dynamics simulations; protein-DESs interactions; stability","en","journal article","","","","","","","","","","","Team Poulumi Dey","","",""
"uuid:3436c42b-024e-4a03-8609-9e35cebf3726","http://resolver.tudelft.nl/uuid:3436c42b-024e-4a03-8609-9e35cebf3726","Stability of backward stochastic differential equations: the general Lipschitz case","Papapantoleon, A. (TU Delft Applied Probability; National Technical University of Athens; Foundation for Research and Technology - Hellas (FORTH)); Possamaï, Dylan (ETH Zürich); Saplaouras, Alexandros (National Technical University of Athens)","","2023","In this paper, we obtain stability results for backward stochastic differential equations with jumps (BSDEs) in a very general framework. More specifically, we consider a convergent sequence of standard data, each associated to their own filtration, and we prove that the associated sequence of (unique) solutions is also convergent. The current result extends earlier contributions in the literature of stability of BSDEs and unifies several frameworks for numerical approximations of BSDEs and their implementations.","BSDE; nonlinear martingale representations; processes with jumps; random time horizon; stability; stochas-tically discontinuous martingales; stochastic Lipschitz generator","en","journal article","","","","","","","","","","","Applied Probability","","",""
"uuid:ec523c08-c21a-44ca-a79b-abf34f10f7dd","http://resolver.tudelft.nl/uuid:ec523c08-c21a-44ca-a79b-abf34f10f7dd","Impact of the Current on Reverse Bias Degradation of Perovskite Solar Cells","Henzel, J. (TU Delft Photovoltaic Materials and Devices; TNO); Bakker, N.J. (TNO); Najafi, Mehrdad (TNO); Zardetto, Valerio (TNO); Veenstra, Sjoerd (TNO); Isabella, O. (TU Delft Photovoltaic Materials and Devices); Mazzarella, L. (TU Delft Photovoltaic Materials and Devices); Weeber, A.W. (TU Delft Photovoltaic Materials and Devices; TNO); Theelen, Mirjam (TNO)","","2023","Nonequal current generation in the cells of a photovoltaic module, e.g., due to partial shading, leads to operation in reverse bias. This quickly causes a significant efficiency loss in perovskite solar cells. We report a more quantitative investigation of the reverse bias degradation. Various small reverse biases (negative voltages) were applied for different durations. After normalizing the applied voltages with the breakdown voltages, we found similar dependences of the reverse bias current and the degradation rate. We draw conclusions regarding possible degradation mechanisms and propose a way to increase the comparability of degradation rates for comparing different perovskite solar cells.","degradation; negative voltages; partial shading; perovskite solar cells; reverse bias; stability","en","journal article","","","","","","","","","","","Photovoltaic Materials and Devices","","",""
"uuid:f75e6d40-8c00-45c1-add8-399e7f06364f","http://resolver.tudelft.nl/uuid:f75e6d40-8c00-45c1-add8-399e7f06364f","Quantification of Fractional Dynamical Stability of EEG Signals as a Bio-Marker for Cognitive Motor Control","Reed, Emily A. (University of Southern California); Bogdan, Paul (University of Southern California); Gonçalves Melo Pequito, S.D. (TU Delft Team Sergio Pequito)","","2022","Assessing the stability of biological system models has aided in uncovering a plethora of new insights in genetics, neuroscience, and medicine. In this paper, we focus on analyzing the stability of neurological signals, including electroencephalogram (EEG) signals. Interestingly, spatiotemporal discrete-time linear fractional-order systems (DTLFOS) have been shown to accurately and efficiently represent a variety of neurological and physiological signals. Here, we leverage the conditions for stability of DTLFOS to assess a real-world EEG data set. By analyzing the stability of EEG signals during movement and rest tasks, we provide evidence of the usefulness of the quantification of stability as a bio-marker for cognitive motor control.","nonlinear models; stability; EEG signals; control applications; cognitive motor control","en","journal article","","","","","","","","","","","Team Sergio Pequito","","",""
"uuid:8c399d54-9bef-4f08-afb4-cd0d3dded54c","http://resolver.tudelft.nl/uuid:8c399d54-9bef-4f08-afb4-cd0d3dded54c","Investigations of the Virtual Impedance Control Mode of Synchronverter in the Power Swing","Gonzalez-Longatt, Francisco M. (University of South-Eastern Norway); Rueda, José L. (TU Delft Intelligent Electrical Power Grids); Palensky, P. (TU Delft Intelligent Electrical Power Grids); Chamorro, Harold R. (KTH Royal Institute of Technology)","","2022","Power electronic converter (PEC) is a key element for the successful integration of novel technologies, PEC working as inverter at novel generation technologies are the decisive components to zero-net carbon emissions in the electricity systems. The colossal penetration of IBG tends to produce several issues in the power networks. There is a tendency to agree that the voltage source converters (VSCs) empowered with the so-called grid forming (GFR) control may provide a long-term solution for the inverter-based generation-dominated power systems. This scientific paper presents an investigation (based on numerical simulations) of the effect of the virtual impedance control mode of one grid forming control technique in the power swing of power systems. Numerical time-domain simulations on test systems are used to assess the effect of the virtual impedance (VI) control mode of the synchronverter (SynC) during a power swing. In both cases, the simulation-based investigation has shown evidence of using high and low virtual impedance in both cases, considering constant impedance and proportional over-current limitation. However, this paper concludes that further assessments are required.","converters; control; power swing; stability; virtual impedance","en","conference paper","IEEE","","","","","Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care 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.","","2023-03-28","","","Intelligent Electrical Power Grids","","",""
"uuid:80a003c4-76d6-4bbf-83ff-063e619a64ed","http://resolver.tudelft.nl/uuid:80a003c4-76d6-4bbf-83ff-063e619a64ed","Induced aseismic slip and the onset of seismicity in displaced faults","Jansen, J.D. (TU Delft Civil Engineering & Geosciences); Meulenbroek, B.J. (TU Delft Mathematical Physics)","","2022","We address aseismic fault slip and the onset of seismicity resulting from depletion-induced or injection-induced stresses in reservoirs with pre-existing vertical or inclined faults. Building on classic results, we discuss semi-analytical modelling techniques for fault slip including dislocation theory, Cauchy-type singular integral equations and the use of Chebyshev polynomials for their solution and an eigenvalue-based stability analysis. We consider slip patch development during depletion for faults with zero, constant static and slip-weakening friction, and our results confirm earlier findings based on numerical simulation, in particular the aseismic growth of two slip patches that may subsequently merge and/or become unstable resulting in nucleation of seismic slip. New findings include improved approximate expressions for the induced seismic moment per unit strike length and a description of the effect of coupling between the slip patches which affects both forward simulation and eigenvalue computation for high values of the ratio of fault throw to reservoir height. Our implementation based on analytical inversion and semi-analytical integration with Chebyshev polynomials is more efficient and more robust than our numerical integration approach. It is not yet well suited for Monte Carlo simulation, which typically requires sub-second simulation times, but with some further development that option seems to be within reach. Moreover, our results offer a possibility for embedded fault modelling in large-scale numerical simulation tools.","Keywords: Chebyshev polynomial; semi-analytical; singular integral; stability","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care 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.","","2022-11-07","Civil Engineering & Geosciences","","Mathematical Physics","","",""
"uuid:544ac73d-9b05-4593-a038-f21a3687ad0d","http://resolver.tudelft.nl/uuid:544ac73d-9b05-4593-a038-f21a3687ad0d","Multiscale analysis for traveling-pulse solutions to the stochastic fitzhugh–nagumo equations","Eichinger, Katharina (Université Paris-Dauphine); Gnann, M.V. (TU Delft Analysis); Kuehn, Christian (Technische Universität München)","","2022","We investigate the stability of traveling-pulse solutions to the stochastic FitzHugh–Nagumo equations with additive noise. Special attention is given to the effect of small noise on the classical deterministically stable fast traveling pulse. Our method is based on adapting the velocity of the traveling wave by solving a scalar stochastic ordinary differential equation (SODE) and tracking perturbations to the wave meeting a system of a scalar stochastic partial differential equation (SPDE) coupled to a scalar ordinary differential equation (ODE). This approach has been recently employed by Krüger and Stannat (Nonlinear Anal. 162 (2017) 197–223) for scalar stochastic bistable reaction–diffusion equations such as the Nagumo equation. A main difference in our situation of an SPDE coupled to an ODE is that the linearization has essential spectrum parallel to the imaginary axis and thus only generates a strongly continuous semigroup. Furthermore, the linearization around the traveling wave is not self-adjoint anymore, so that fluctuations around the wave cannot be expected to be orthogonal in a corresponding inner product. We demonstrate that this problem can be overcome by making use of Riesz instead of orthogonal spectral projections as recently employed in a series of papers by Hamster and Hupkes in case of analytic semigroups. We expect that our approach can also be applied to traveling waves and other patterns in more general situations such as systems of SPDEs with linearizations only generating a strongly continuous semigroup. This provides a relevant generalization as these systems are prevalent in many applications.","FitzHugh–Nagumo equations; pulse; stability; stochastic reaction–diffusion equations; traveling waves","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care 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.","","2023-07-01","","","Analysis","","",""
"uuid:99dc4a89-524a-4740-95f0-bf3af94012a9","http://resolver.tudelft.nl/uuid:99dc4a89-524a-4740-95f0-bf3af94012a9","An Interface Co-modification Strategy for Improving the Efficiency and Stability of CsPbI3Perovskite Solar Cells","Guan, Hui (Lanzhou University); Lei, Yutian (Lanzhou University); Wu, Qiyuan (Lanzhou University); Zhou, Xufeng (Liaocheng University); Wang, H. (TU Delft Photovoltaic Materials and Devices); Wang, Gang (Ningbo University); Li, Wenquan (Qinghai Normal University); Jin, Zhiwen (Lanzhou University); Lan, Wei (Lanzhou University)","","2022","Interface engineering is a simple and effective strategy for improving the photovoltaic performance and stability of perovskite solar cells (PSCs). Herein, an interface co-modification strategy is proposed, using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and 2-fluoro-1,4-phenylenediammonium iodide (2FPPD) to modify the electron transport layer (ETL)/perovskite (PVK) and the PVK/hole transport layer (HTL) interfaces, respectively. A series of characterizations demonstrate that the PCBM&2FPPD interface co-modification strategy effectively enhances the extraction and transport efficiency of carriers at the interface, passivates surface defects, inhibits the nonradiative recombination of carriers, and simultaneously inhibits ion migration. Moreover, this strategy improves the crystallinity and surface hydrophobicity of PVK and optimizes the energy level alignment of PSCs. As a result, all photovoltaic parameters are improved after optimization, where the power conversion efficiency (PCE) of PSCs has increased from 17.01% to 18.36%. Meanwhile, the optimized PSCs show excellent environmental stability, which can be stably stored in air (RH = 10-20%) for about 800 h.","CsPbI; defect passivation; interface engineering; perovskite solar cell; photovoltaic performance; stability","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care 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.","","2023-04-27","","","Photovoltaic Materials and Devices","","",""
"uuid:d382bbdd-4718-406a-89eb-bd6b76d7cdde","http://resolver.tudelft.nl/uuid:d382bbdd-4718-406a-89eb-bd6b76d7cdde","Stability Region Exploring of Shunt Active Power Filters Based on Output Admittance Modeling","Lei, Jintao (Zhejiang University); Qin, Z. (TU Delft DC systems, Energy conversion & Storage); Li, Wuhua (Zhejiang University); Bauer, P. (TU Delft DC systems, Energy conversion & Storage); He, Xiangning (Zhejiang University)","","2021","A shunt active power filter (SAPF) is coupled with load admittance in weak grid conditions, which poses a challenge to stability analysis. In this article, the admittance model of the SAPF is developed, which reveals the coupling mechanism between SAPF and load concisely and accurately. On top of that, the stability region of the system is investigated. The passivity region of the load admittance to guarantee the system stability is first explored. However, the passivity region has a very narrowband at a specific frequency, which makes it difficult to achieve. The stability region is then studied and it turns out to be an extension of the passivity region, and especially the narrowband is expanded. Therefore, the stability region is much easier to meet. The stability-oriented design is then summarized in a flowchart. In the end, the effectiveness of the newly defined stability region is verified by experimental results.","Admittance; Harmonic analysis; Impedance; Load modeling; Power harmonic filters; Power system stability; Thermal stability; active power filters; admittance; modeling; stability; Active power filters","en","journal article","","","","","","","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:cdf0d2e3-edc6-455f-befe-7c9d4595ba80","http://resolver.tudelft.nl/uuid:cdf0d2e3-edc6-455f-befe-7c9d4595ba80","Directed evolution of unspecific peroxygenase in organic solvents","Martin-Diaz, Javier (Institute of Catalysis, CSIC, Madrid); Molina-Espeja, Patricia (Institute of Catalysis, CSIC, Madrid); Hofrichter, Martin (Technische Universität Dresden); Hollmann, F. (TU Delft BT/Biocatalysis); Alcalde, Miguel (Institute of Catalysis, CSIC, Madrid)","","2021","Fungal unspecific peroxygenases (UPOs) are efficient biocatalysts that insert oxygen atoms into nonactivated C–H bonds with high selectivity. Many oxyfunctionalization reactions catalyzed by UPOs are favored in organic solvents, a milieu in which their enzymatic activity is drastically reduced. Using as departure point the UPO secretion mutant from Agrocybe aegerita (PaDa-I variant), in the current study we have improved its activity in organic solvents by directed evolution. Mutant libraries constructed by random mutagenesis and in vivo DNA shuffling were screened in the presence of increasing concentrations of organic solvents that differed both in regard to their chemical nature and polarity. In addition, a palette of neutral mutations generated by genetic drift that improved activity in organic solvents was evaluated by site directed recombination in vivo. The final UPO variant of this evolutionary campaign carried nine mutations that enhanced its activity in the presence of 30% acetonitrile (vol/vol) up to 23-fold over PaDa-I parental type, and it was also active and stable in aqueous acetone, methanol and dimethyl sulfoxide mixtures. These mutations, which are located at the surface of the protein and in the heme channel, seemingly helped to protect UPO from harmful effects of cosolvents by modifying interactions with surrounding residues and influencing critical loops.","activity; directed evolution; fungal unspecific peroxygenases; organic solvents; Saccharomyces cerevisiae; stability","en","journal article","","","","","","","","","","","BT/Biocatalysis","","",""
"uuid:53a890f3-335c-4fd6-947d-5fc1903f20bb","http://resolver.tudelft.nl/uuid:53a890f3-335c-4fd6-947d-5fc1903f20bb","Framework for Studying Stability of Switching Max-Plus Linear Systems","Gupta, A. (TU Delft Team Bart De Schutter); van den Boom, A.J.J. (TU Delft Team Bart De Schutter); van der Woude, J.W. (TU Delft Mathematical Physics); De Schutter, B.H.K. (TU Delft Team Bart De Schutter)","","2020","We propose a framework for studying the stability of discrete-event systems modelled as switching max-plus linear systems. In this framework, we propose a set of notions of stability for generic discrete-event systems in the max-plus algebra. Then we show the loss of equivalence of these notions for switching max-plus linear systems due to the lack of global monotonicity and the accompanying difficulty in rigorous analysis. This serves as a motivation to relax the assumption on monotonicity of the dynamics to positive invariance of max-plus cones. Then we proceed to generalise the notions of stability when the dynamics is restricted to such cones. The stability analysis approach presented in this paper serves as a first step to study the stability of a general class of switching max-plus linear systems.","Discrete event systems; max-plus algebra; switching; stability; invariance","en","journal article","","","","","","","","","","","Team Bart De Schutter","","",""
"uuid:7f0ae54b-520f-43b7-84a1-839559423792","http://resolver.tudelft.nl/uuid:7f0ae54b-520f-43b7-84a1-839559423792","Hypericin: Source, Determination, Separation, and Properties","Zhang, Jie (Chongqing Technology and Business University); Gao, Ling (Chongqing Technology and Business University); Hu, Jie (Chongqing Technology and Business University); Wang, Chongjun (Chongqing Technology and Business University); Hagedoorn, P.L. (TU Delft BT/Biocatalysis); Li, Ning (Chongqing Technology and Business University); Zhou, Xing (Chongqing Academy of Chinese Materia Medica, Chongqing)","","2020","Hypericin is a naturally occurring compound synthesized by certain species of the genus Hypericum, with various pharmacological effects. It is used as a natural photosensitizing agent with great potential in photodynamic therapy. This review discusses the latest results about the biosynthetic pathways and chemical synthetic routes to obtain hypericin. Although many analysis methods can be used for the determination of hypericin purity, HPLC has become the method of choice due to its fast and sensitive analyses. The extraction and purification of hypericin are also described. Hypericin can be used as a photosensitizer due to a large and active π-electron conjugated system in its structure. Medical applications of hypericin are not easy due to several unsolved practical problems, which include hypericin phototoxicity, poor solubility in water, and extreme sensitivity to light, heat, and pH.","extraction; Hypericin; photosensitivity; solubility; stability; synthesis","en","journal article","","","","","","","","","","","BT/Biocatalysis","","",""
"uuid:77784d7c-8f01-4222-bb83-87ee1de52930","http://resolver.tudelft.nl/uuid:77784d7c-8f01-4222-bb83-87ee1de52930","In-plane dynamics of high-speed rotating rings on elastic foundation","Lu, T. (TU Delft Railway Engineering)","Metrikine, A. (promotor); Tsouvalas, A. (copromotor); Delft University of Technology (degree granting institution)","2019","Rotating ring-like structures are very commonly used in civil, mechanical and aerospace engineering. Typical examples of such structures are components in turbomachinery, compliant gears, rolling tyres and flexible train wheels. At the micro-scale, rotating ring models find their applications in the field of ring gyroscopes, in which high accuracy of modelling is required. The in-plane vibrations of rotating rings are of particular interest since such structural components are usually subject to in-plane loads. The focus in this thesis is therefore placed on the in-plane dynamics of rotating rings. While the radial and circumferential motions of a stationary ring are coupled due to curvature, a steadily rotating ring, as any gyroscopic system, is subject to two additional fictitious forces induced by the gyroscopic coupling due to rotation, i.e. the Coriolis and centrifugal forces. Among them the centrifugal force associated with the steady rotation of the ring (quasi-static force) introduces an axi-symmetric radial expansion and a hoop stress; the latter has the tendency to stiffen the ring. In contrast, the dynamic part of the centrifugal force has the tendency to soften the system. Next to that, the Coriolis force bifurcates the natural frequencies of the ring. The proper consideration of the rotation effects is essential to determine the dynamic behaviour of rotating rings, such as stability of free vibrations and resonance of rotating rings under stationary loads. Although various models exist, the considerations of rotation effects are not always in agreement, resulting in distinct theoretical predictions of critical speeds associated with instability and resonance of rotating rings. In addition, in all the existing rotating ring models, the equations of motion were derived assuming the inner and outer surfaces of the ring to be traction-free. However, when one considers a ring whose inner surface is elastically restrained by distributed springs, this assumption is violated. The traction at the inner surface can significantly influence the stress distribution along the thickness of the ring and this effect has to be properly accounted for since the internal stresses may show a strong gradient from the inner surface to the outer surface, especially in the case of rings rotating at high speeds or when the latter are supported by stiff foundation. The primary aim of this thesis is to develop a highly accurate rotating ring model that properly accounts for both the rotation and boundary effects with rigorous mathematical derivation to fill the gap regarding the modelling and prediction of the dynamic behaviour of high-speed rotating rings. To achieve this aim, the following four objectives are set: (i) identify the reasons of disagreements between various existing rotating ring models and clarify the mathematically sound derivations of governing equations; (ii) develop a high-order rotating ring model which properly accounts for the rotation effects, as well as the non-zero tractions at boundaries; (iii) close the debate on the prediction of critical speeds associated with instability of free vibrations and resonance of forced vibrations; and (iv) apply the developed high-order model to predict the steadystate response of rotating rings under stationary loads and the stability of rotating ringstationary oscillator system.","high-speed; rotating rings; elastic foundation; in-plane vibration; stability; high-order theory; traction boundary effects; critical speeds; steady-state response; ring-oscillator system","en","doctoral thesis","","978-94-6323-850-2","","","","","","2020-02-01","","","Railway Engineering","","",""
"uuid:cb0b0207-8df5-40fc-ab99-9fe5939f780a","http://resolver.tudelft.nl/uuid:cb0b0207-8df5-40fc-ab99-9fe5939f780a","A Reinforcement Learning Approach for Frequency Control of Inverted-Based Microgrids","Adibi, M. (TU Delft Mathematical Physics); van der Woude, J.W. (TU Delft Mathematical Physics)","","2019","In this paper, we present a reinforcement learning control scheme for optimal frequency synchronization in a lossy inverter-based microgrid. Compared to the existing methods in the literature, we relax the restrictions on the system, i.e. being a lossless microgrid, and the transmission lines and loads to have constant impedances. The proposed control scheme does not require a priori information about system parameters and can achieve frequency synchronization in the presence of dominantly resistive and/or inductive line and load impedances, model parameter uncertainties, time varying loads and disturbances. First, using Lyapunov theory a feedback control is formulated based on the unknown dynamics of the microgrid. Next, a performance function is defined based on cumulative rewards towards achieving convergence to the nominal frequency. The performance function is approximated by a critic neural network in real-time. An actor network is then simultaneously learning a parameterized approximation of the nonlinear dynamics and optimizing the approximated performance function obtained from the critic network. The performance of our control scheme is validated via simulation on a lossy microgrid case study in the presence of disturbances.","frequency synchronization; microgrids; reinforcement learning; stability","en","journal article","","","","","","","","","","","Mathematical Physics","","",""
"uuid:935b7fbf-3b06-468b-92cc-722943f8b3ba","http://resolver.tudelft.nl/uuid:935b7fbf-3b06-468b-92cc-722943f8b3ba","The application of Ag/AgCl electrodes as chloride sensors in cementitious materials","Pargar, F. (TU Delft Materials and Environment)","van Breugel, K. (promotor); Koleva, D.A. (copromotor); Delft University of Technology (degree granting institution)","2018","Determination of the chloride content in a reinforced concrete structure is important for evaluation of the risk of chloride-induced corrosion of reinforcement. The traditional techniques for chloride determination in concrete are laborious, time-consuming and cannot be used for continuous monitoring of the chloride content. The investigation on the use of Ag/AgCl electrodes as chloride sensors in cement-based materials dates back to 1990s. Interpretation of the sensor’s response in cementitious materials requires the knowledge of chloride sensor’s characteristics and the interaction between the sensor and the surrounding medium. Hence, the stability of the chloride sensor’s response in cementitious materials depends on the properties of Ag/AgCl interface, AgCl/cement paste interface and the pore solution composition of cementitious materials. The influence of these factors on the stability of the sensor’s response was studied in this thesis. In Chapter 1 the background and motivation for the thesis were presented. In Chapter 2 the advantages and drawbacks of available test methods for determination of the chloride content in cementitious materials were explained.","Ag/AgCl electrode; chloride sensor; anodization; open circuit potential; stability; alkalinity; interference; hydration product; corrosion of steel","en","doctoral thesis","","978-94-6186-972-2","","","","","","","","","Materials and Environment","","",""
"uuid:4e63aefa-04cf-4a63-a5b0-e48d6e227390","http://resolver.tudelft.nl/uuid:4e63aefa-04cf-4a63-a5b0-e48d6e227390","Scheduling under uncertainty: Attaining flexibility, robustness and stability","Mountakis, Kiriakos Simon (TU Delft Algorithmics)","Witteveen, C. (promotor); Klos, T.B. (copromotor); Delft University of Technology (degree granting institution)","2018","The research presented in this thesis is part of the Rolling Stock Life Cycle Logistics applied research and development program, conducted by NedTrain. As a company, NedTrain belongs to Nederlandse Spoorwegen (NS; the principal railway company in the Netherlands) and provides maintenance services for the NS train-fleet. The aim of this program is to enhance NedTrain’s competitiveness as a rolling-stock maintenance services provider. Our work focuses on the operational aspects of this R&D program, motivated by the challenge of scheduling tasks (or operations) in a NedTrain maintenance workshop, such that trains are delivered on-time for circulation in the rail network. Most tasks in the workshop have uncertain durations (or processing times), which complicates the scheduling process.","simple temporal network; flexibility; robustness; stability; scheduling under encertainty; resource constrained project scheduling; monte carlo sampling","en","doctoral thesis","","","","","","","","","","","Algorithmics","","",""
"uuid:f611f70c-8308-4522-a95a-31599778fe1e","http://resolver.tudelft.nl/uuid:f611f70c-8308-4522-a95a-31599778fe1e","Some effects of crosswind on the lateral dynamics of a bicycle","Schwab, A.L. (TU Delft Biomechatronics & Human-Machine Control); Dialynas, G. (TU Delft Biomechatronics & Human-Machine Control); Happee, R. (TU Delft Intelligent Vehicles)","Espinosa, Hugo G. (editor); Rowlands, David R. (editor); Shepherd, Jonathan (editor); Thiel, David V. (editor)","2018","The bicycle, being unstable at low speed and marginally stable at high speed, is sensitive to lateral perturbations. One of the major lateral perturbations is crosswind, which can lead to accidents and fatalities. Here we investigate the effect of crosswind on the lateral dynamics and control of the bicycle in a wide range of forward speeds and various crosswinds, by means of computer model analysis and simulation. A low dimensional bicycle model is used together with experimentally identified rider control parameters. The crosswind forces are obtained from a recent experimental study. Analysis and simulation show that crosswind decreases the stability of the bicycle and is clearly a safety issue.","bicycle; crosswind; dynamics; control; stability; handling","en","conference paper","MDPI","","","","","","","","","","Biomechatronics & Human-Machine Control","","",""
"uuid:1d12467a-aae9-4a64-bec1-7e21aa58d642","http://resolver.tudelft.nl/uuid:1d12467a-aae9-4a64-bec1-7e21aa58d642","Effects of Substrate and Polymer Encapsulation on CO2 Electroreduction by Immobilized Indium(III) Protoporphyrin","Birdja, Yuvraj Y. (Universiteit Leiden); Vos, Rafaël E. (Universiteit Leiden); Wezendonk, T.A. (TU Delft ChemE/Catalysis Engineering); Jiang, Lin (Universiteit Leiden); Kapteijn, F. (TU Delft ChemE/Catalysis Engineering); Koper, M.T.M. (Universiteit Leiden)","","2018","Heterogenization of molecular catalysts for CO2 electroreduction has attracted significant research activity, due to the combined advantages of homogeneous and heterogeneous catalysts. In this work, we demonstrate the strong influence of the nature of the substrate on the selectivity and reactivity of electrocatalytic CO2 reduction, as well as on the stability of the studied immobilized indium(III) protoporphyrin IX, for electrosynthesis of formic acid. Additionally, we investigate strategies to improve the CO2 reduction by tuning the chemical functionality of the substrate surface by means of electrochemical and plasma treatment and by catalyst encapsulation in polymer membranes. We point out several underlying factors that affect the performance of electrocatalytic CO2 reduction. The insights gained here allow one to optimize heterogenized molecular systems for enhanced CO2 electroreduction without modification of the catalyst itself.","activity; CO electroreduction; immobilization; polymer encapsulation; pretreatment effect; selectivity; stability; substrate effect","en","journal article","","","","","","","","","","","ChemE/Catalysis Engineering","","",""
"uuid:aedf23cb-a2d4-49e7-8244-1524aa6e0de3","http://resolver.tudelft.nl/uuid:aedf23cb-a2d4-49e7-8244-1524aa6e0de3","Magnetic Detumbling of Fast-tumbling Picosatellites","Fonod, R. (TU Delft Space Systems Egineering); Gill, E.K.A. (TU Delft Space Engineering; TU Delft Space Systems Egineering)","","2018","The problem of pure magnetic detumbling of a fast-tumbling picosatellite is considered. A new weighted B-dot control algorithm is proposed. The algorithm enables power reduction while not sacrificing detumbling performance. Analytical expressions relating the maximal expected rotational rate to the minimum sampling time required are presented. Simulation results demonstrate the practical benefits of the proposed approach for picosatellites.","Picosatellite; magnetic detumbling; B-dot; attitude control; stability","en","conference paper","International Astronautical Federation, IAF","","","","","","","","","Space Engineering","Space Systems Egineering","","",""
"uuid:61343c83-e1a9-4af7-ba4c-357ce2c1f44d","http://resolver.tudelft.nl/uuid:61343c83-e1a9-4af7-ba4c-357ce2c1f44d","Design and implementation of a steer-by-wire bicycle","Dialynas, G. (TU Delft Biomechatronics & Human-Machine Control); Happee, R. (TU Delft Intelligent Vehicles); Schwab, A.L. (TU Delft Biomechatronics & Human-Machine Control)","","2018","Since the 1800s, the design of bicycles involves a mechanical linkage between the handlebar and the fork assembly. Herein, we propose an innovation, where the traditional mechanical connection between the handlebar and fork is decoupled and replaced with sensors, servomo-tors and a microcontroller allowing artificial manipulation of the bicycle and steering dynamics. The purpose of our steer-by-wire bicycle is to investigate the influence of handlebar torque feedback on rider control in order to understand rider control on a bicycle. In addition, steer-by-wire bicycles have the potential to be used as stability-enhancing support systems which can improve cycling safety. We demonstrate the design and performance of the steer-by-wire bicycle in computer simulations as well as real-life tests. Preliminary rider tests showed a per-ceived near-to-identical behaviour of the steer-by-wire system to a mechanical connection at steering frequencies below 3 Hz.","bicycle; steer-by-wire; stability; control; rider control","en","conference paper","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care 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.","","2019-05-01","","","Biomechatronics & Human-Machine Control","","",""
"uuid:b6797eb5-537c-4a6c-b7a1-b7d18081fea1","http://resolver.tudelft.nl/uuid:b6797eb5-537c-4a6c-b7a1-b7d18081fea1","Stability and Decentralized Control of Plug-and-Play DC Distribution Grids","van der Blij, N.H. (TU Delft DC systems, Energy conversion & Storage); Ramirez Elizondo, L.M. (TU Delft DC systems, Energy conversion & Storage); Spaan, M.T.J. (TU Delft Algorithmics); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2018","Changes in distribution grids pose significant challenges with respect to the control and management of these grids. Stability and decentralized control are vital to ensure the availability and accessibility of plug-and-play dc distribution grids that are (temporarily) without communication. Therefore, this paper presents guidelines for these grids that ensure global stability and a decentralized control strategy that implements these stability guidelines. The stability guidelines are derived using a Brayton-Moser representation of the system to arrive at a Lyapunov candidate function. Furthermore, the decentralized control strategy implements these stability guidelines and ensures that the voltages in the system remain within a specified range. Additionally, several simulations are performed to illustrate the stability of the system and the behavior of the control strategy under different scenarios.","DC distribution grid; Decentralized control; decentralised control; Guidelines; Impedance; microgrid; plug-and-play; Power system stability; stability; Stability criteria; Topology","en","journal article","","","","","","","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:025c6de2-9cb1-473d-b9c4-ff7574cb766a","http://resolver.tudelft.nl/uuid:025c6de2-9cb1-473d-b9c4-ff7574cb766a","Boron doping induced thermal conductivity enhancement of water-based 3C-Si(B)C nanofluids","Li, Bin (University of Science and Technology Beijing); Jiang, Peng (University of Science and Technology Beijing); Zhai, Famin (University of Science and Technology Beijing); Chen, Junhong (University of Science and Technology Beijing); Bei, G. (TU Delft (OLD) MSE-1; University of Science and Technology Beijing); Hou, Xinmei (University of Science and Technology Beijing); Chou, Kuo Chih (University of Science and Technology Beijing)","","2018","In this paper, the fabrication and thermal conductivity (TC) of water-based nanofluids using boron (B)-doped SiC as dispersions are reported. Doping B into the β-SiC phase leads to the shrinkage of the SiC lattice due to the substitution of Si atoms (0.134 nm radius) by smaller B atoms (0.095 nm radius). The presence of B in the SiC phase also promotes crystallization and grain growth of obtained particles. The tailored crystal structure and morphology of B-doped SiC nanoparticles are beneficial for the TC improvement of the nanofluids by using them as dispersions. Using B-doped SiC nanoparticles as dispersions for nanofluids, a remarkable improvement in stability was achieved in SiC-B6 nanofluid at pH 11 by means of the Zeta potential measurement. By dispersing B-doped SiC nanoparticles in water-based fluids, the TC of the as-prepared nanofluids containing only 0.3 vol.% SiC-B6 nanoparticles is remarkably raised to 39.3% at 30 °C compared to the base fluids, and is further enhanced with the increased temperature. The main reasons for the improvement in TC of SiC-B6 nanofluids are more stable dispersion and intensive charge ions vibration around the surface of nanoparticles as well as the enhanced TC of the SiC-B dispersions.","boron doping; SiC nanofluids; stability; thermal conductivity","en","journal article","","","","","","Accepted Author Manuscript","","2019-06-22","","","(OLD) MSE-1","","",""
"uuid:a5190c45-516a-472e-9580-9c088df5dc86","http://resolver.tudelft.nl/uuid:a5190c45-516a-472e-9580-9c088df5dc86","First Tests on the Symmetrical Breakwater Armor Unit Crablock","Salauddin, M (Chittagong University of Engineering and Technology; IHE Delft Institute for Water Education); Broere, A.; van der Meer, J.W. (IHE Delft Institute for Water Education); Verhagen, H.J. (TU Delft Coastal Engineering); Bijl, E (CDR International)","","2017","Single layer concrete armor systems are being widely used nowadays in the design of rubble mound breakwaters. Recently, a new concrete armor unit has been developed and applied as single layer armor system in the repair works of one damaged breakwater at Al Fujeirah, UAE. It has a symmetrical shape, in contrast to most other units. Modern single layer concrete armor units that exist at this moment have design guidelines in terms of placement, stability and overtopping. However, because of lack of laboratory research and the little experience of using Crablock, no design guidance exists yet for this new single layer block compared to other existing one layer units. Being a new armor unit, the placement was investigated first. Then physical model tests were performed in a wave flume to come up with results on stability and wave overtopping. Furthermore, to determine the interlocking properties of armor units, pull tests were also conducted in this research. The placement tests showed that uniform placement was best achieved with a rectangular grid on a relatively small underlayer of rock. Test results on stability showed that longer waves affected the armor layer a little more, with more rocking and earlier start of damage. Packing density as well as placement pattern showed no influence on wave overtopping. The overtopping tests gave larger overtopping than expected, which might be due to the fairly steep 1:30 foreshore that gave a large ratio of significant wave-height from the time domain and the spectral wave-height.","Crablock; placement pattern; single layer armor; stability; wave overtopping","en","journal article","","","","","","","","2019-02-01","","","Coastal Engineering","","",""
"uuid:b884841b-a00b-47e2-be24-f9f897479fe9","http://resolver.tudelft.nl/uuid:b884841b-a00b-47e2-be24-f9f897479fe9","Takagi–Sugeno fuzzy payload estimation and adaptive control","Beyhan, Selami (Pamukkale University); Eghbal Sarabi, F. (TU Delft Support Delft Center for Systems and Control); Lendek, Zsofia (Technical University of Cluj-Napoca); Babuska, R. (TU Delft Learning & Autonomous Control)","","2017","In this paper, a novel adaptive Takagi-Sugeno (TS) fuzzy observer-based controller is proposed. The closed-loop stability and the boundedness of all the signals are proven by Lyapunov stability analysis. The proposed controller is applied to a flexible-transmission experimental setup. The performance for constant payload in the presence of noisy measurements is compared to a controller based on a classical extended Luenberger observer. Simulation and real-time results show that the proposed observer-based feedback controller provides accurate position tracking under constant and varying payloads.","adaptive payload estimation; flexible-transmission system; observer-based control; stability; TS fuzzy modeling","en","journal article","","","","","","","","","","","Support Delft Center for Systems and Control","","",""
"uuid:0e1304bb-c405-42ea-8b25-730bd9e36e61","http://resolver.tudelft.nl/uuid:0e1304bb-c405-42ea-8b25-730bd9e36e61","Voltage Control in Distributed Generation under Measurement Falsification Attacks","Ma, M. (TU Delft Intelligent Electrical Power Grids); Herdeiro Teixeira, A.M. (TU Delft Information and Communication Technology); van den Berg, Jan (TU Delft Cyber Security; TU Delft Information and Communication Technology); Palensky, P. (TU Delft Intelligent Electrical Power Grids)","","2017","Low-voltage distribution grids experience a rising penetration of inverter-based, distributed generation. In order to not only contribute to but also solve voltage problems, these inverters are increasingly asked to participate in intelligent grid controls. Communicating inverters implement distributed voltage droop controls. The impact of cyber-attacks to the stability of such distributed grid controls is poorly researched and therefore addressed in this article. We characterize the potential impact of several attack scenarios by employing the positivity and diagonal dominance properties. In particular, we discuss measurement falsification scenarios where the attacker corrupts voltage measurement data received by the voltage droop controllers. Analytical, control-theoretic methods for assessing the impact on system stability and voltage magnitude are presented and validated via simulation.","Cyber security; distribution network; risk assessment; stability; voltage control","en","journal article","","","","","","","","","","","Intelligent Electrical Power Grids","","",""
"uuid:541ca256-235b-45f6-bb91-9dac09c7880d","http://resolver.tudelft.nl/uuid:541ca256-235b-45f6-bb91-9dac09c7880d","Stability of DC Distribution Systems: An Algebraic Derivation","van der Blij, N.H. (TU Delft DC systems, Energy conversion & Storage); Ramirez Elizondo, L.M. (TU Delft DC systems, Energy conversion & Storage); Spaan, M.T.J. (TU Delft Algorithmics); Bauer, P. (TU Delft DC systems, Energy conversion & Storage)","","2017","Instability caused by low inertia and constant power loads is a major challenge of DC distribution grids. Previous research uses oversimplified models or does not provide general rules for stability. Therefore, a comprehensive approach to analyze the stability of DC distribution systems is desired. This paper presents a method to algebraically analyze the stability of any DC distribution system through the eigenvalues of its state-space matrices. Furthermore, using this method, requirements are found for the stability of three example systems. Additionally, a sensitivity analysis is performed, which considers the effect of several system parameters on the stability and disputes some overgeneralized conclusions of previous research. Moreover, various simulations are performed to illustrate the dynamic behavior of a stable and an unstable DC distribution system.","DC distribution; eigenvalues; sensitivity analysis; stability; state-space","en","journal article","","","","","","","","","","","DC systems, Energy conversion & Storage","","",""
"uuid:f23d3a76-9962-4f16-be8c-dab3bdfdb884","http://resolver.tudelft.nl/uuid:f23d3a76-9962-4f16-be8c-dab3bdfdb884","Security Evaluation of the Cyber Networks under Advanced Persistent Threats","Yang, L. (TU Delft Network Architectures and Services); Li, Pengdeng (Chongqing University); Yang, Xiaofan (Chongqing University); Tang, Yuan Yan (University of Macau)","","2017","Advanced persistent threats (APTs) pose a grave threat to cyberspace, because they deactivate all the conventional cyber defense mechanisms. This paper addresses the issue of evaluating the security of the cyber networks under APTs. For this purpose, a dynamic model capturing the APT-based cyber-attack-defense processes is proposed. Theoretical analysis shows that this model admits a globally stable equilibrium. On this basis, a new security metric known as the equilibrium security is suggested. The impact of several factors on the equilibrium security is revealed through theoretical analysis or computer simulation. These findings contribute to the development of feasible security solutions against APTs.","Cyberspace; measurement; nonlinear dynamical systems; security; stability","en","journal article","","","","","","","","","","","Network Architectures and Services","","",""
"uuid:e35c4735-1f6f-4e4c-b7b8-130f68a7dd02","http://resolver.tudelft.nl/uuid:e35c4735-1f6f-4e4c-b7b8-130f68a7dd02","Reducing the cover-to-diameter ratio for shallow tunnels in soft soils","Vu, M.N. (TU Delft Geo-engineering)","Bosch, J.W. (promotor); Broere, W. (copromotor); Delft University of Technology (degree granting institution)","2016","Despite the fact that shallow tunnels have the benefits of low short-term construction costs and long-term operational costs primarily due to the shallow depth of the station boxes, the limited understanding of shallow tunnelling in soft soils is an obstacle to the development of shallow tunnels in urban areas. This study carries out a theoretical investigation of the effects of reducing the cover-to-diameter ratio C/D for shallow tunnels in soft soils.
In stability analysis, the uplift, face stability and blow-out mechanisms are investigated. This study investigates interactions between the TBM and surrounding soil in tunnelling process, the stability of the TBM is not taken into account. The relationship between the C/D ratio and the required thickness-to-diameter ratio d/D as well as the required support pressures will be derived in various soils. Ranges of support pressures are also estimated for the TBM.
Structural analysis is carried out for the variation of deformations and internal forces of the tunnel lining when reducing the C/D ratio. Since the conventional design models are not suitable in the case of shallow tunnels a new structural analysis model, which includes the difference between loads at the top and at the bottom of the tunnel, is proposed. Optimal C/D ratios with various d/D ratios for shallow tunnels in soft soils are also derived.
With respect to ground movement analysis, this research investigates the areas affected by shallow tunnelling with a preliminary assessment of the risk of building damage by investigating surface and subsurface soil displacements. These areas are determined for different tunnel diameters in various soil types and are then compared to recent studies.
The total volume loss is estimated at the tunnelling face, along the TBM, at the tail and includes long-term consolidation settlements. By combining empirical models from the literature and the proposed new models, the volume loss components are estimated both for short-term construction and for the long-term consolidation effects. This shows that a no volume loss is feasible in shallow tunnelling with careful control of the support pressure.
The boundaries of the influence zones in shallow tunnelling are identified and discussed on the basis of various case studies. The effects of the soil parameters on the influence areas are also investigated.
From these calculations, the limits and optimal C/D ratios for shallow tunnelling are deduced and recommendations and solutions for improving the shallow tunnelling process are proposed in this dissertation.