Andrea Ballerini
We consider the inverse problem of the detection of a single body, immersed in a bounded container filled with a fluid which obeys the Stokes equations, from a single measurement of force and velocity on a portion of the boundary. We obtain an estimate of stability of log-log type.
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Inspired by the numerical immersed boundary method, we introduce regularized Stokes immersed boundary problems in two dimensions to describe regularized motion of a 1-D closed elastic string in a 2-D Stokes flow, in which a regularized $δ$-function is used to mollify the flow field and singular forcing. We establish global well-posedness of the regularized problems, and prove that as the regularization parameter diminishes, string dynamics in the regularized problems converge to that in the Stokes immersed boundary problem with no regularization. Viewing the un-regularized problem as a benchma…
We study coupled motion of a 1-D closed elastic string immersed in a 2-D Stokes flow, known as the Stokes immersed boundary problem in two dimensions. Using the fundamental solution of the Stokes equation and the Lagrangian coordinate of the string, we write the problem into a contour dynamic formulation, which is a nonlinear non-local equation solely keeping track of evolution of the string configuration. We prove existence and uniqueness of local-in-time solution starting from an arbitrary initial configuration that is an $H^{5/2}$-function in the Lagrangian coordinate satisfying the so-call…
The Immersed Inextensible Interface Problem in 2D Stokes Flow
本文研究二维Stokes流中受弯曲力作用的不可伸长闭合界面动力学，以切角建立边界积分方程并证明其适定性与光滑性，通过数值计算初步探讨界面长时间行为。
We study the motion of a 1-D closed elastic string with bending and stretching energy immersed in a 2-D Stokes flow. In this paper we introduce the curve's tangent angle function and the stretching function to describe the deferent deformations of the elastic string. These two functions are defined on the arc-length coordinate and the material coordinate respectively. With the help of the fundamental solution of the Stokes equation, we reformulate the problem into a parabolic system which is called the contour dynamic system. Under the non-self-intersecting and well-stretched assumptions on in…
We consider the inverse problem of the detection of a single body, immersed in a bounded container filled with a fluid which obeys the stationary Navier-Stokes equations, from a single measurement of force and velocity on a portion of the boundary. We obtain an estimate of stability of log-log type.
Asymptotic flocking dynamics of Relativistic-Cucker-Smale particles immersed in incompressible Navier-Stokes equations
研究提出 Relativistic Cucker-Smale 粒子与不可压缩 Navier-Stokes 方程通过阻力耦合的系统，证明其在 $\mathbb{T}^3$ 上的全局弱解存在性及特定条件下的指数对齐。
We consider the problem of a one dimensional elastic filament immersed in a two dimensional steady Stokes fluid. Immersed boundary problems in which a thin elastic structure interacts with a surrounding fluid are prevalent in science and engineering, a class of problems for which Peskin has made pioneering contributions. Using boundary integrals, we first reduce the fluid equations to an evolution equation solely for the immersed filament configuration. We then establish local well-posedness for this equation with initial data in low-regularity Hölder spaces. This is accomplished by first extr…
The Immersed Boundary Problem in 2-D: the Navier-Stokes Case
本文研究了二维浸没边界问题中纳维-斯托克斯方程的解的存在性、唯一性和正则性，探讨了雷诺数趋近于零时的收敛性及能量守恒条件。
From the steady Stokes and Navier-Stokes models, a penalization method has been considered by several authors for approximating those fluid equations around obstacles. In this work, we present a justification for using fictitious domains to study obstacles immersed in incompressible viscous fluids through a simplified version of Brinkman's law for porous media. If the scalar function $ψ$ is considered as the inverse of permeability, it is possible to study the singularities of $ψ$ as approximations of obstacles (when $ψ$ tends to $\infty$) or of the domain corresponding to the fluid (when $ψ= …
A free boundary problem for an immersed filament in 3D Stokes flow
本文研究三维Stokes流中浸没细丝的自由边界问题，通过角平均NtD算子分解证明简化演化方程为三阶抛物方程且局部适定，为细长体近似计算奠定数学基础。
We consider the motion of a rigid body immersed in a two-dimensional viscous incompressible fluid with Navierslip-with-friction conditions at the solid boundary. The fluid-solid system occupies the whole plane. We provethe small-time exact controllability of the position and velocity of the solid when the control takes the form of adistributed force supported in a compact subset (with nonvoid interior) of the fluid domain, away from the body.The strategy relies on the introduction of a small parameter: we consider fast and strong amplitude controls forwhich the ``Navier-Stokes+rigid body'' sys…
Uniform error estimates for Navier-Stokes flow with an exact moving boundary using the immersed interface method
本文研究低雷诺数纳维-斯托克斯流中精确移动边界问题，利用浸入界面法实现有限差分法的均匀二阶精度，证明速度误差为O(h²|log h|²)，压力误差为O(h²|log h|³)。
Determination of time dependent source terms for Stokes systems in unbounded domains
本文研究无界区域中Stokes系统时间依赖向量值源项的唯一确定问题，利用唯一延拓、近似可控性与复分析等方法，并给出重建算法和数值算例。
On the collective effect of a large system of heavy particles immersed in a Newtonian fluid
该研究针对有界域内牛顿流体中的大质量重粒子系统，分析半径趋于零、质量密度以适当速率趋于无穷的重粒子的集体效应，证明其与Navier-Stokes系统均匀化过程中的Brinkman摄动具有相似性。
Consider an inextensible closed filament immersed in a 2D Stokes fluid. Given a force density $\mathbf{F}$ defined on this filament, we consider the problem of determining the tension $σ$ on this filament that ensures the filament is inextensible. This is a subproblem of dynamic inextensible vesicle and membrane problems, which appear in engineering and biological applications. We study the well-posedness and regularity properties of this problem in Hölder spaces. We find that the tension determination problem admits a unique solution if and only if the closed filament is {\em not} a circle. F…
In this work we are interested in estimating the size of a cavity D immersed in a bounded domain Ω, contained in R^d, d=2,3, filled with a viscous fluid governed by the Stokes system, by means of velocity and Cauchy forces on the external boundary of Ω. More precisely, we establish some lower and upper bounds in terms of the difference between the external measurements when the obstacle is present and without the object. The proof of the result is based on interior regularity results and quantitative estimates of unique continuation for the solution of the Stokes system.
We prove a null controllability result for the Vlasov-Navier-Stokes system, which describes the interaction of a large cloud of particles immersed in a fluid. We show that one can modify both the distribution of particles and the velocity field of the fluid from any initial state to the zero steady state, by means of an internal control. Indeed, we can modify the non-linear dynamics of the system in order to absorb the particles and let the fluid at rest. The proof is achieved thanks to the return method and a Leray-Schauder fixed-point argument.
A nonlocal curve evolution for an immersed elastic filament: global existence and convergence to resistive force theory
研究非局部曲线演化模型，证明其在能量空间中的全局存在性，并展示其在ε→0时收敛到阻力理论。
Boundary determination of the Riemannian metric from Cauchy data for the Stokes equations
该研究针对带光滑边界的紧致连通黎曼流形，证明Stokes方程的柯西数据可唯一确定流形边界上黎曼度量的所有阶偏导数，为相关逆问题研究提供理论支撑。
Stress concentration between two adjacent rigid particles in Navier-Stokes flow
本文研究Navier-Stokes流中两个相邻凸刚性粒子间的应力集中问题，在二维和三维情形下建立了速度梯度与二阶导数的精确上下界，证明爆破速率最优，并分析了Cauchy应力的爆破行为。
On a model of an elastic body fully immersed in a viscous incompressible fluid with small data
针对浸没在两层不可压缩粘性流体间的弹性体模型，由阻尼波动方程与Navier-Stokes方程耦合，建立了小初始数据下的全局时间适定性与指数衰减，并证明最终状态除水平小位移外必为平凡。
Asymmetric equilibrium configurations of a body immersed in a 2D laminar flow
本文研究二维层流通道中可能非对称物体的流固耦合平衡问题，在防止碰撞的适当假设下证明小流入/流出时平衡构型存在唯一，并给出对称性成立的条件。
Velocity optimization of self-equilibrated obstacles in a two-dimensional viscous flow
研究二维粘性流中障碍物的自平衡条件，并通过形状变化优化其平移和角速度，在测度论框架下重新定义自平衡概念。
We consider the Stokes system in $\mathbb R^3,$ deprived of $N$ spheres of radius $1/N,$ completed by constant boundary conditions on the spheres. This problem models the instantaneous response of a viscous fluid to an immersed cloud of moving solid spheres. We assume that the centers of the spheres and the boundary conditions are given randomly and we compute the asymptotic behavior of solutions when the parameter $N$ diverges. Under the assumption that the distribution of spheres/centers is chaotic, we prove convergence in mean to the solution of a Stokes-Brinkman problem.
We propose a mathematical derivation of Brinkman's force for a cloud of particles immersed in an incompressible fluid. Our starting point is the Stokes or steady Navier-Stokes equations set in a bounded domain with the disjoint union of N balls of radius 1/N removed, and with a no-slip boundary condition for the fluid at the surface of each ball. The large N limit of the fluid velocity field is governed by the same (Navier-)Stokes equations in the whole domain, with an additional term (Brinkman's force) that is (minus) the total drag force exerted by the fluid on the particle system. This can …
Stability of a Two-Phase Stokes Problem with Surface Tension
本文研究同黏度两相二维 Stokes 气泡在表面张力下的适定性，证明近圆初始轮廓存在唯一全局解并指数收敛至圆，且低正则扰动随后瞬时解析化。
Reconstruction of obstacles in a Stokes flow as a shape-from-moments problem
本文将平面 Stokes 流障碍物位置与形状的边界测量反问题转化为 shape-from-moments 问题，并通过专用重建方法在数值实验中取得显著优于现有文献方法的效果。
In this paper we study the motion of a rigid body driven by Newton's law immersed in a stationary incompressible Stokes flow occupying a bounded simply connected domain. The aim is that of trajectory tracking of the solid by the means of a control in the form of Dirichlet boundary data on the outside boundary of the fluid domain. We show that it is possible to exactly achieve any smooth trajectory for the solid that stays away from the external boundary, by the means of such a remote control. The proof relies on some density methods for the Stokes system, as well as a reformulation of the soli…
This paper studies global existence, hydrodynamic limit, and large-time behavior of weak solutions to a kinetic flocking model coupled to the incompressible Navier-Stokes equations. The model describes the motion of particles immersed in a Navier-Stokes fluid interacting through local alignment. We first prove the existence of weak solutions using energy and $L^p$ estimates together with the velocity averaging lemma. We also rigorously establish a hydrodynamic limit corresponding to strong noise and local alignment. In this limit, the dynamics can be totally described by a coupled compressible…
We study the problem where a one-dimensional elastic string is immersed in a two-dimensional steady Stokes fluid. This is known as the Stokes immersed boundary problem and also as the Peskin problem. We consider the case with equal viscosities and with a fully non-linear tension law; this model has been called the fully nonlinear Peskin problem. In this case we prove local in time well-posedness for arbitrary initial data in the scaling critical Besov space $\dot{B}^{3/2}_{2,1}(\mathbb{T} ; \mathbb{R}^2)$. We additionally prove the optimal higher order smoothing effects for the solution. To pr…
A theory for the evolution of a metric $g$ driven by the equations of three-dimensional continuum mechanics is developed. This metric in turn allows for the local existence of an evolving three-dimensional Riemannian manifold immersed in the six-dimensional Euclidean space. The Nash-Kuiper theorem is then applied to this Riemannian manifold to produce a wild evolving $C^{1}$ manifold. The theory is applied to the incompressible Euler and Navier-Stokes equations. One practical outcome of the theory is a computation of critical profile initial data for what may be interpreted as the onset of tur…
This work is concerned with the necessary conditions of optimality for a minimal time control problem $(P)$ for the linearized Navier-Stokes periodic flow in a 2D-channel, subject to a boundary input which acts on the transversal component of the velocity. The objective in this problem is the reaching of the laminar regime in a minimum time, as well as its preservation after this time. The determination of the necessary conditions of optimality relies on the analysis of intermediate minimal time control problems $(P_{k})$ for the Fourier modes $"k"$ associated to the Navier-Stokes equations an…
Towards a computational framework using finite element methods with Arbitrary Lagrangian-Eulerian approach for swimmers with contact
本文提出了一个基于带ALE框架的有限元方法的计算框架，用于模拟浸没在Navier-Stokes流体中的多个不同几何形状游泳者的运动，并通过基于Feel++库的数值实验验证了其适应性。
We consider a stochastic perturbation of the phase field alpha-Navier-Stokes model with vesicle-fluid interaction. It consists in a system of nonlinear evolution partial differential equations modeling the fluid-structure interaction associated to the dynamics of an elastic vesicle immersed in a moving incompressible viscous fluid. This system of equations couples a phase-field equation -- for the interface between the fluid and the vesicle -- to the alpha-Navier-Stokes equation -- for the viscous fluid -- with an extra nonlinear interaction term, namely the bending energy. The stochastic pert…
We introduce a new method for constructing solenoidal extensions of fairly general boundary data in (2d or 3d) cubes that contain an obstacle. This method allows us to provide explicit bounds for the Dirichlet norm of the extensions. It runs as follows: by inverting the trace operator, we first determine suitable extensions, not necessarily solenoidal, of the data; then we analyze the Bogovskii problem with the resulting divergence to obtain a solenoidal extension; finally, by solving a variational problem involving the infinity-Laplacian and using ad hoc cutoff functions, we find explicit bou…
We consider a mathematical model for the interactions of an elastic body fully immersed in a viscous, incompressible fluid. The corresponding composite PDE system comprises a linearized Navier-Stokes system and a dynamic system of elasticity; the coupling takes place on the interface between the two regions occupied by the fluid and the solid, respectively. We specifically study the regularity of boundary traces (on the interface) for the fluid velocity field. The obtained trace regularity theory for the fluid component of the system -- of interest in its own right -- establishes, in addition,…
Consider a rigid body ${\mathcal S} \subset {\mathbb R}^3$ immersed in an infinitely extended Navier-Stokes liquid and the motion of the body-fluid interaction system described from a reference frame attached to ${\mathcal S}$. We are interested in steady motions of this coupled system, where the region occupied by the fluid is the exterior domain $Ω= {\mathbb R}^3 \setminus {\mathcal S}$. This paper deals with the problem of using boundary controls $v_*$, acting on the whole $\partialΩ$ or just on a portion $Γ$ of $\partialΩ$, to generate a self-propelled motion of ${\mathcal S}$ with a targe…
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