CFD Modelling and Simulation
http://hdl.handle.net/20.500.11824/7
2023-02-03T13:42:35ZLimited Visual Range in the Social Force Model: Effects on Macroscopic and Microscopic Dynamics
http://hdl.handle.net/20.500.11824/1538
Limited Visual Range in the Social Force Model: Effects on Macroscopic and Microscopic Dynamics
García, A.; Hernández-Delfin, D.; Lee, D.-J.; Ellero, M.
The Social Force Model has been widely used to simulate pedestrian dynamics. Its simplicity and ability to reproduce some collective patterns of behavior make it an adequate tool in the field of pedestrian dynamics. However, its ability to reproduce common macroscopic empirical results, such as pedestrian flows through a bottleneck and the speed-density fundamental diagram, has scarcely been studied. In addition, the effect of each parameter of the model on the dynamics of the system has rarely been shown. In this contribution, a comprehensive parameter-sensitivity analysis in the social force model is provided, and an optimal set is introduced, capable of reproducing both macroscopic experimental flow data and collision avoidance between pedestrians in simple trajectories on the microscopic scale. We show that the incorporation of asymmetric visual range models in the inter-pedestrian
interactions is required for quantitative agreement. The model is also capable of showing collision avoidance in simple pedestrian trajectories and lane formation in non-crowded bidirectional pedestrian flows.
2023-01-15T00:00:00ZA numerical method for suspensions of articulated bodies in viscous flows
http://hdl.handle.net/20.500.11824/1523
A numerical method for suspensions of articulated bodies in viscous flows
Balboa, F.; Delmotte, B.
An articulated body is defined as a finite number of rigid bodies connected by a set of arbitrary constraints that limit the relative motion between pairs of bodies. Such a general definition encompasses a wide variety of situations in the microscopic world, from bacteria to synthetic micro-swimmers, but it is also encountered when discretizing inextensible bodies, such as filaments or membranes. In this work we consider hybrid articulated bodies, i.e. constituted of both linear chains, such as filaments, and closed-loop chains, such as membranes. Simulating suspensions of such articulated bodies requires to solve the hydrodynamic interactions between large collections of objects of arbitrary shape while satisfying the multiple constraints that connect them. Two main challenges arise in this task: limiting the cost of the hydrodynamic solves, and enforcing the constraints within machine precision at each time-step. To address these challenges we propose a formalism that combines the body mobility problem in Stokes flow with a velocity formulation of the constraints, resulting in a mixed mobility-resistance problem. While resistance problems are known to scale poorly with the particle number, our preconditioned iterative solver is not sensitive to the system size, therefore allowing to study large suspensions with quasilinear computational cost. Additionally, constraint violations, e.g. due to discrete time-integration errors, are prevented by correcting the particles' positions and orientations at the end of each time-step. Our correction procedure, based on a nonlinear minimisation algorithm, has negligible computational cost and preserves the accuracy of the time-integration scheme. The versatility of our method allows to study a plethora of articulated systems within a unified framework. We showcase its robustness and scalability by exploring the locomotion modes of a model microswimmer inspired by the diatom colony Bacillaria Paxillifer, and by simulating large suspensions of bacteria interacting near a no-slip boundary. Finally, we provide a Python implementation of our framework in a collaborative publicly available code, where the user can prescribe a set of constraints through a single input file to study a wide spectrum of applications involving suspensions of articulated bodies.
2022-09-01T00:00:00ZTechnology-Agnostic Assessment of Wave Energy System Capabilities
http://hdl.handle.net/20.500.11824/1511
Technology-Agnostic Assessment of Wave Energy System Capabilities
Ruiz‐minguela, P.; Blanco, J.M.; Nava, V.; Jeffrey, H.F.
Developing new wave energy technologies is risky, costly and time-consuming. The large diversity of concepts, components and evaluation criteria creates a vast design space of potentially feasible solutions. This paper aims to introduce a novel methodology for the holistic assessment of wave energy capabilities in various market applications based on sound Systems Engineering methods. The methodology provides a consistent hierarchy of performance metrics relevant to the given system of reference, design activity and development stage under consideration as a means to scrutinise wave energy requirements. Full traceability of system requirements and performance metrics is then facilitated by multi-criteria decision tools and aggregation logic, respectively. The qualitative assessment in the case studies has resulted in very different rankings of System Drivers and Stakeholders for the two market applications considered. However, the Stakeholder Requirements and Functional Requirements present a small variation in the weights for the two application markets which results in a quantitative assessment with very similar Global Merit. Finally, the performance benchmark using the Commercial Attractiveness and Technical Achievability concepts enables a more objective comparison in the utility-scale and remote generation markets and a way to concentrate innovation efforts before proceeding to the next development stage.
2022-04-01T00:00:00ZExperimental investigation of anomalous molecular probe diffusion in entangled polymer melts
http://hdl.handle.net/20.500.11824/1510
Experimental investigation of anomalous molecular probe diffusion in entangled polymer melts
Nieto, D.; Ramakrishnan, V.; Smoukov, S. K.; Venerus, D. C.
Investigations on the diffusion of small molecules or particles in polymeric materials are important to numerous technologies and can also be used to gain insight on polymer chain dynamics. Systems where the probe size is comparable to (or smaller than) a characteristic length of the polymer chain, the tube diameter for example, are of particular interest because the diffusion coefficient of the probe can be orders of magnitude larger than the value predicted by the Stokes-Einstein relation. In the present study, we employ the optical technique known as forced Rayleigh scattering to study the diffusion of a molecular probe (dye) in several entangled polymer melts over a wide range of length and time scales. The probe size is much smaller than the tube diameter for the systems studied. We find the diffusion coefficient is larger by four to five orders of magnitude than the Stokes-Einstein prediction. More interestingly, we observe anomalous, non-Fickian, diffusion where the value of the measured diffusion coefficient can abruptly change by as much as 50%. We suggest that this unexpected behavior occurs when the time scale for diffusion is larger than the relaxation time associated with the constraint release mechanism for polymer chain dynamics.
2022-01-01T00:00:00Z