Active matter: a multiscale simulation method for advanced swimmers
Project Leader: Ellie Hajizadeh
Primary Contact: Ellie Hajizadeh (email@example.com)
Keywords: complex fluids; computational fluid dynamics; fluid dynamics; micro-fluidics; soft matter
Disciplines: Biomedical Engineering,Chemical & Biomolecular Engineering,Mechanical Engineering
Introduction and importance
Artificial soft swimmers have emerged as a safe alternative solution to rigid swimmers in a wide range of applications such as minimally-invasive microsurgery, sensing in soft robotics, and localised drug delivery, in which the rigid swimmers could result in a catastrophic damage to the host media. . While various methods have been applied for Computational Fluid Dynamics (CFD) simulation of these swimmers, the lack of an accurate model to capture the multiscale nature of the underlying physical phenomena dictating their flow behavior hinders the effective design of these swimmers. We propose a novel multiscale numerical model which is a combination of Smooth Particle Hydrodynamics (SPH) approach and Stochastics Smoothed Dissipative Particle Dynamics (SDPD) to capture the incompressible fluid flow as well as thermal fluctuations of the swimmers. This model, as the results of these methods show , can simulate the free surface of the immersed boundary of the swimmer and will have an accurate solution for the incompressible fluid flow.
Background and literature review
Engels et al.  presented a numerical simulation of simplified models for swimming organisms or robots using chord-wise flexible plates. We focus on the tip vortices originating from three-dimensional effects due to the finite span of the plate. These effects play an important role when predicting the swimmer’s cruising velocity, since they contribute significantly to the drag force. Also, Stricker  investigated the behavior of a single artificial swimmer namely an active droplet moving by Marangoni flow. He provided a numerical treatment for the main factors playing a role in real systems, such as advection, diffusion and the presence of chemical species with different behaviors. Volpe and Gigan  used a mathematical model for their motion using a set of stochastic differential equations and a numerical simulation method, corresponding set of finite difference equations both in homogenous and complex environments. Teran et al.  studied the effect of a complex medium upon swimmer’s locomotion as well as investigated numerically the effect of fluid viscoelasticity on the dynamics of an undulating swimming sheet.
Objectives and contributions
One of the most important obstacles for the design of swimmers is the lack of a robust numerical model to be able to couple the macroscopic Navier-Stokes formalism and mesoscale deformation of the swimmer’s body. The main objective of this research is to address this critical gap in our knowledge through developing a multiscale simulation platform. This multiscale simulation platform will enable us to effectively capture the underlying physical phenomena which will result in enhanced design tool for advanced swimmers. Development of such a powerful simulation and modelling tool will enable scientists and engineers to take promising step in application areas such as wireless control, sensing and navigating through complex different media. After the fundamental study of this new model and validation, we will combine our numerical model with an optimisation algorithm. Differential Evolution (DE) algorithm , which is an efficient algorithm in optimisation will applied for this step. Therefore, the last aim of our modeling is optimisation of the involved parameters of the swimmer for better controlling its motion in interaction with incompressible fluid flow.
In previous studies the arbitrary Lagrangian-Eulerian method  was utilised to couple the deformation of the swimmer’s body equations to the fluid flow equations, although this novel approach is limited in accurate simulation of the swimmer’s body formation. In this study, the motion of the swimmer and incompressible fluid flow will be modelled through the Smoothed Dissipative Particle Dynamics (SDPD) method, which is a discretised Lagrangian representation of Navier-Stokes equations with thermal fluctuations. Based on the swimmer deformation, we will encountered with large mesh deformation in our simulation, so we will need to apply a new approach to capture this phenomena.
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