52 research outputs found
The magnitude of the intrinsic rate constant: How deep can association reactions be in the diffusion limited regime?
No full textIntrinsic and effective rate constants have an important role in the theory of diffusion-limited reactions. In a previous paper, we provide detailed microscopic expressions for these intrinsic rates [A. Vijaykumar, P. G. Bolhuis, and P. R. ten Wolde, Faraday Discuss. 195, 421 (2016)], which are usually considered as abstract quantities and assumed to be implicitly known. Using these microscopic expressions, we investigate how the rate of association depends on the strength and the range of the isotropic potential and the strength of the non- specific attraction in case of the anisotropic potential. In addition, we determine the location of the interface where these expressions become valid for anisotropic potentials. In particular, by investigating the particles' orientational distributions, we verify whether the interface at which these distributions become isotropic agrees with the interface predicted by the effective association rate constant. Finally, we discuss how large the intrinsic association rate can become, and what are the consequences for the existence of the diffusion limited regime. Published by AIP Publishing
Stranggjutningssimulering med Smoothed Particle Hydrodynamics
No full textThis thesis proposes a way of simulating the continuous casting process of steel using Smoothed Particle Hydrodynamics (SPH). It deals with the SPH modeling of mass, momentum and the energy equations. The interpolation kernel functions required for the SPH modeling of these equations are calculated. Solidification is modeled by some particles are used to represent fluids and others solids. Elastic forces are calculated between the particle neighbors to create deformable bodies. The fluid solidifies into the elastic body when it cools down and the elastic body melts as it is heated. In continuous casting the molten metal solidifies forming a shell when it comes in contact with the cold wall. The mold of the continuous casting is modeled with a cold oscillating wall and a symmetric wall. Once the shell is formed water is sprayed on the solidified metal. If the shell is thin and cooling is not sufficient, the elastic body melts due to the effect of the hot fluid.Den klassiska SPH-modellen för vätskor med fri yta kompletteras med värmeledning med fasomvandling och stelning: partiklar kan byta mellan vätske-tillstånd och solid-tillstånd beroende på temperaturen. Elastiska krafter beroende på avstånd mellan partiklarna aktiveras i solid-tillståndet och slås av i fluid-tillstånd så att vätskan kan stelna och senare smälta igen om så behövs. Vid stränggjutning stelnar smältan, som fylls på via ett rör, vid kontakt med en oscillerande, kall kokill-vägg, till ett elastiskt skal. Detta kyls fortlöpande genom påsprutning av vatten utanpå kokillen och direkt på skalet, som förångas. Skalet deformeras nedanför kokillen av det hydrostatiska trycket från smältan; om det ar för tunt brister det. Som demonstration gjordes en simulering där ett skal skapas, varpå man slår av vattenkylningen på ett parti: då smälter skalet och blir tunnare och till sist brister det och all smälta rinner ut genom hålet. Noggrannheten i simuleringen lämnar en del att önska men det vore mycket svårt att bygga en så komplex modell med vanlig CFD
Multiscale simulations of anisotropic particles combining molecular dynamics and Green's function reaction dynamics
No full textThe modeling of complex reaction-diffusion processes in, for instance, cellular biochemical networks or self-assembling soft matter can be tremendously sped up by employing a multiscale algorithm which combines the mesoscopic Green’s Function Reaction Dynamics (GFRD) method with explicit stochastic Brownian, Langevin, or deterministic molecular dynamics to treat reactants at the microscopic scale [A. Vijaykumar, P. G. Bolhuis, and P. R. ten Wolde, J. Chem. Phys. 143, 214102 (2015)]. Here we extend this multiscale MD-GFRD approach to include the orientational dynamics that is crucial to describe the anisotropic interactions often prevalent in biomolecular systems. We present the novel algorithm focusing on Brownian dynamics only, although the methodology is generic. We illustrate the novel algorithm using a simple patchy particle model. After validation of the algorithm, we discuss its performance. The rotational Brownian dynamics MD-GFRD multiscale method will open up the possibility for large scale simulations of protein signalling networks
Focused laser spike dewetting as a method to probe rheology of polymer thin films
No full textThin polymer films whose thickness ranges from fractions of a nanometer to several micrometers have been in high demand over the past few years in several industries. Their high surface area to volume ratio and the potential for low-cost processing with minimal material usage while fulfilling purpose requirements make them very useful. However, these films behave differently from bulk materials and majority of polymer fabrication processes involve polymer flow. Hence the study of polymer thin film rheology becomes crucial. Bulk measurement of rheology is well established, but it has disadvantages in that it requires a lot of material and may not capture thin film physics. Previous studies have demonstrated dewetting of thin polymer films to study film material stability and properties. This study seeks to use focused laser spike (FLaSk) dewetting as a method to probe rheology of thin material films. The method is used to extract materials properties of three thin films – Polystyrene (PS), Poly –4–hydroxystyrene (PHS) and N, N′-Bis (3 – methylphenyl)–N, N′-diphenylbenzidine (TPD) having different glass transition temperatures,M.S.Includes bibliographical referencesby Adithya Sridha
Open-Domain Aspect-Opinion Co-Mining with Double-Layer Span Extraction
No full textThe aspect-opinion extraction tasks extract aspect terms and opinion terms from reviews. The supervised extraction methods achieve state-of-the-art performance but require large-scale human-annotated training data. Thus, they are restricted for open-domain tasks due to the lack of training data. This work addresses this challenge and simultaneously mines aspect terms, opinion terms, and their correspondence in a joint model. We propose an Open-Domain Aspect-Opinion Co-Mining (ODAO) method with a Double-Layer span extraction framework. Instead of acquiring human annotations, ODAO first generates weak labels for unannotated corpus by employing rules-based on universal dependency parsing. Then, ODAO utilizes this weak supervision to train a double-layer span extraction framework to extract aspect terms (ATE), opinion terms (OTE), and aspect-opinion pairs (AOPE). ODAO applies canonical correlation analysis as an early stopping indicator to avoid the model over-fitting to the noise to tackle the noisy weak supervision. ODAO applies a self-training process to gradually enrich the training data to tackle the weak supervision bias issue. We conduct extensive experiments and demonstrate the power of the proposed ODAO. The results on four benchmark datasets for aspect-opinion co-extraction and pair extraction tasks show that ODAO can achieve competitive or even better performance compared with the state-of-the-art fully supervised methods.This proceeding is published as Mohna Chakraborty, Adithya Kulkarni, and Qi Li. 2022. Open-Domain Aspect-Opinion Co-Mining with Double-Layer Span Extraction. In Proceedings of the 28th ACM SIGKDD Conference on Knowledge Discovery and Data Mining (KDD '22). Association for Computing Machinery, New York, NY, USA, 66–75. https://doi.org/10.1145/3534678.3539386. © 2022 Copyright held by the owner/author(s). This work is licensed under a Creative Commons Attribution International 4.0 License
A new coupled modelling framework for turbine inflow generation: mesoscale-synthetic turbulence
No full textAt the mercy of strong winds, high wind shear, unstable boundary layer and anomalous atmospheric conditions, stands a wind turbine designed to produce sustainable power under harsh conditions. The field of wind energy is a promising prospect for a sustainable future. Diverse research towards the improvement of a wind turbine’s capability and cost is currently the focus of the wind energy industry. With higher wind turbines being designed every day, various challenges and limitations of the current state-of-the-art surface; anomalous atmospheric conditions, structural integrity and cost.The goal of this thesis is to extend the approach to design a site-specific wind turbine considering an anomalous atmospheric condition. By coupling a mesoscale model with a stochastic turbulence function, a wind field capable of depicting a particular atmospheric condition is created. Using an aeroelastic solver the resulting loads on a wind turbine can be simulated. The methodology uses Weather, Research and Forecasting (WRF) model to re-create an event of low-level jet identified at the met mast of FINO-1, off coast Germany. The wind profile is coupled with a stochastic turbulence function designed at FINO-1 to be used as wind field for the aeroelastic solver, FAST.A literature survey identified a multitude of approaches used for simulating a low-level jet and analyse the loads on a wind turbine, the majority of which indicate high computational costs and contrived re-creations of the event. Thus, the challenge was to identify a near-realistic event creation with low computational costs. Therefore, coupling a low-resolution mesoscale model to create the event with a site-specific stochastic turbulence function is used to analyse loads on a wind turbine. Meteorological data analysis at FINO-1 led to the identification of three case studies of low-level jets under varied stability conditions of the atmosphere. The case studies are compared with the International Electrotechnical Commission (IEC) standard’s, IEC – 61400 – Ed3; IEC Kaimal and IEC Great Planes Low Level Jet (GPLLJ) spectrum. For cases with high stability, on an average proposed model predicts 21% higher stress on blade root and 27% higher at the tower top and base in comparison to IEC GPLLJ and 15% and 30% lower in comparison to IEC Kaimal, respectively. Similarly, under unstable conditions, proposed model predicts similar loads on the blade root, 7% lower loads at the tower top and base in comparison to IEC GPLLJ and 30% higher loads for blade root and tower top and base in comparison to IEC Kaimal. Comparing these results with literature on high stability loading higher loads are expected under these conditions.Concluding, this project developed a model framework to analyse anomalous atmospheric phenomena on a wind turbine specific to a site with low computational costs. While the capabilities of the model have been successfully showcased, only a partial validation on a benchmark case has been carried out. Therefore, going forward a full physical validation of the model for its accuracy for its target applications is recommended.Electrical Engineering | Sustainable Energy Technolog
Aerodynamic assessment of sub-scale aircraft model: A multi-fidelity approach
No full textNovel designs like the Flying-V, Prandtl-Plane and Blended Wing-Body show promise towards sustainable aviation. In the preliminary design phase, Sub-scale Flight Test (SFT) is a reliable method to get insight into the flight behavior of these designs. The effectiveness and value provided by SFT depends on the similitude between the SFT model and the full-scale aircraft. The method ofcomputational scaling is a state-of-the-art method into designing SFT models, that maximizes the similitude. However, this method is often infeasible because of large computational costs. Of the various analyses in this methodology, the aerodynamic analysis is computationally most expensive. Therefore, this research developed a multi-fidelity approach for the assessment of aerodynamiccharacteristics of SFT model. The approach utilized a blend of Reynolds- Averaged Navier-Stokes (RANS) and 3D-Panel Method (3DPM). This provided a good tradeoff between accuracy and computational cost, making the method of computational scaling a feasible method into design of SFT models.Aerospace Engineerin
Evaluating the feasibility of studying propeller-wing interaction through ground-based high-speed experimental taxi-tests: A numerical study comparing a propeller powered aircraft in cruising free-flight with high-speed taxiing
No full textThe Dutch Electric Aviation Centre possesses and uses a Cessna Skymaster 337F as an experimental flying testbed to help gain knowledge to aid the transition towards hybrid/ electric aviation. The interaction between the rear propeller slipstream and the horizontal tail has been likened to the interaction of propeller-wing configurations seen on larger regional aircraft. The DEAC intends to study this interaction through ground-based high-speed taxi-tests before any flight tests. By doing so, tests are conducted in a safer and more accessible environment without the need for re-certification, albeit, with changes to both testing environment and aircraft operational settings. This numerical study focused on evaluating the feasibility of such a testing approach to help gain an insight and better prepare for experiments. RANS CFD studies were performed on a simplified self-designed and developed half-airplane half-propeller model of the aircraft in ground-run configuration and free-flight configuration. In this stead-state simulation, the propellers were treated as actuator disks and had a specified constant pressure rise. Vortices being shed from the fuselage and interacting with the tail were discovered. The uncertainties due to the chosen simplifications, the neglect of twin contra-rotating propeller swirls, and the fact that the formation and evolution of the wake vortices, and their interaction with both the rear propeller and the horizontal tail are inherently unsteady effects, precludes a definitive conclusion. A more detailed numerical model is required to address the situation and evaluate the feasibility of this approach.Dutch Electric Aviation CenterAerospace Engineerin
Optimal Charging Strategies for Electric Vehicle Fleets
No full textElectric vehicles are a fast-growing market in the automotive sector. In addition, the widespread use of renewable energy to power electric vehicles makes them sustainable, with considerably low greenhouse gas emissions. As a result, service providers are switching to fleets of electric vehicles to promote environmental sustainability. However, unlike conventional vehicles, EVs require unique infrastructure to charge them. This leads to some technical and economic challenges. Therefore, intelligent charging strategies are needed to charge EV fleets optimally.The thesis primarily focuses on minimizing the energy and battery degradation costs for a fleet operator using different charging strategies. To accomplish this objective, a joint optimization technique is used to solve the problem. The method used is an optimal exchange problem that works by clearing market constraints. Specifically, an ADMM-based distributed charging problem is used for charging the EV fleet. The algorithm is implemented for different charger power levels for the different strategies to analyze the difference in energy and battery degradation costs. Furthermore, a variable charger allocation method is proposed to charge the EV fleet.Mechanical Engineering | Systems and Contro
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