arXiv subjects

Timo Reis

Publications and source records attributed to Timo Reis.

At least 19 recordsLinked to original sources

arXiv2026

Well-posedness and passivity for a class of bilinear control systems

We study an abstract class of bilinear infinite-dimensional systems that arises in various applications, including district heating systems and quantum control. First, we analyze the existence of mild and classical solutions for abstract bilinear systems with admissible input operators in Banach spaces and study continuous dependence on the data. When the underlying space is a Hilbert space, these results are used to show passivity for a suitably defined co-located output and for mild solutions. The results are applied to the bilinear Schr\"odinger equation, the Fokker--Planck equation, and a district heating or cooling pipe.

math.AP↗

arXiv2026

Prescribed-performance position tracking for infinite-dimensional passive systems

We study funnel control for linear infinite-dimensional passive systems whose controlled output is obtained by integrating the passive output. In mechanical applications, this corresponds to position control based on a measured passive velocity output. Within the system-node framework, we propose a nonlinear recursive funnel controller with a dynamic gain supervisor for systems with distributed or boundary control and observation. The supervisor automatically increases a damping gain whenever the normalized recursive error approaches a prescribed monitoring level. The controller uses the tracking error and its derivative, with the latter obtained directly from the passive output rather than by numerical differentiation. We prove global existence and uniqueness of the closed-loop trajectory, prescribed funnel performance, and global boundedness of the derivative tracking error and the passive output. Under an additional position-compatible strict dissipativity condition, the supervised gain is increased only finitely many times and eventually becomes constant. Consequently, the gain, the internal state, and the control input are globally bounded, and the recursive-error funnel margin is uniform in time. The results are illustrated by a boundary-actuated Euler-Bernoulli beam with uniformly positive distributed damping.

math.OC↗

arXiv2026

Analysis of a coupled magneto-quasistatic--mechanical model of an eddy current brake

We study a coupled magneto-quasistatic model for an eddy current brake. The model leads to a nonlinear infinite-dimensional differential-algebraic system in which the nonlinearity is structural rather than caused by nonlinear material laws. It is generated by the closed electromechanical feedback loop: the angular momentum determines the velocity of the conducting disk, the velocity and the magnetic field generate motional eddy currents, and these currents induce a Lorentz torque acting back on the rotor. We introduce a finite-dissipation solution concept and prove global existence and uniqueness of weak solutions for initial data given by the magnetic field and the angular momentum, and for inputs given by the supplied coil current and the externally applied torque.

math.AP↗

arXiv2026

Port-Hamiltonian modelling of coupled rigid/flexible multibody systems

We develop a port-Hamiltonian framework for coupled rigid/flexible multibody systems. The rigid dynamics may be nonlinear and subject to configuration and velocity constraints, while the flexible components are described by linear port-Hamiltonian partial differential equations on one-dimensional spatial domains. The subsystems interact through boundary or distributed ports. On the flexible side, the differential operator and its domain remain fixed, whereas state dependence enters only through finite-dimensional coupling components of the Dirac structure. We show that, under a natural surjectivity condition, the port-Hamiltonian interconnection with a modulated Dirac structure of a finite-dimensional rigid subsystem again yields a modulated Dirac structure. The Hamiltonians of the subsystems add, while the internal coupling powers cancel. The framework is illustrated by a planar moving Euler--Bernoulli beam and a slider--crank mechanism with a flexible connecting member.

math.DS↗

arXiv2026

Analysis and funnel control for nonlinear drill strings

We study the output tracking problem for a vertically driven drill string system described by a nonlinear boundary-coupled PDE-ODE model. Solvability analysis of the drill string model is achieved by first casting the model in an abstract boundary value problem involving set-valued operators on an appropriate Hilbert space. The governing equation here consists of evolution and the damping part. Existence of solutions is established within the framework of maximal monotone operators where one first proves that the evolution operator is a linear skew-adjoint operator and the distributed damping term is a Nemytskii relation which is then proven to be maximal monotone. Maximal monotonicity of the combined operator is then a consequence of Rockafellar's theorem. Furthermore, we propose a novel funnel control design that ensures the angular velocity of the drill bit follows a dynamically adjusted reference trajectory, while the tracking error remains confined within a pre-specified performance funnel. The reference adjustment mechanism adapts in response to large wave traveling times that may cause performance degradation. The corresponding feasibility result is illustrated by some simulations.

math.OC↗

arXiv2026

Optimal control of infinite-dimensional dissipative systems

We study the linear-quadratic optimal control problem for infinite-dimensional dissipative systems with possibly indefinite cost functional. Under the assumption that a storage function exists, we show that this indefinite optimal control problem is equivalent to a linear-quadratic optimal control problem with a nonnegative cost functional. We establish the relationship between the corresponding value functions and present the associated operator Lur'e equation. Finally, we illustrate our results with several examples.

math.OC↗

arXiv2025

Differential algebraic system nodes

Infinite-dimensional differential algebraic equations (short DAEs) with input and output are studied. The concepts of operator nodes and system nodes are extended to systems which additionally may include algebraic constraints. Extrapolation spaces are investigated for differential-algebraic equations, and solutions of the extrapolated DAE are characterized using augmented Wong sequences. The resulting theory is then applied to characterize infinite-dimensional port-Hamiltonian DAEs.

math.AP↗

arXiv2025

Analysis of coupled Maxwell-cable problems

Building on the recently published work "Modeling of radiating curved cables via coupled telegrapher's and Maxwell's equations", which introduces a model for the interaction between electromagnetic fields and radiating (possibly curved) cables, we analyze the qualitative properties of the resulting dynamical system. The model features inputs and outputs given by the currents and voltages at the cable ends, while the state comprises the corresponding distributions along the cables and the electromagnetic fields in the surrounding domain. We show that the autonomous dynamics (i.e., with zero input) generate a strongly continuous semigroup and establish sufficient conditions for well-posedness, meaning continuous dependence of the state and output trajectories on the inputs and initial conditions.

math.AP↗

arXiv2025

Abstract second-order boundary control systems

We consider abstract second order systems of the form $\ddot{x}(t) + D \dot{x}(t) + Sx(t)=0$, which are typically analyzed via the operator matrix $\mathcal{A}=\left[\begin{smallmatrix} 0 & I \\ -S & -D \end{smallmatrix}\right]$ governing the free dynamics of the corresponding first-order in time formulation. While previous work (e.g. on spectral properties of) $\mathcal{A}$ has focused on self-adjoint uniformly positive $S$, we consider the more general case which comprises the situation where $S^*$ is symmetric, i.e., $S^*\subset S$. As we will show, this relaxation allows for a large freedom in view of boundary conditions. Our main contribution is the construction of a boundary triplet for the operator $\mathcal{A}$ and the definition of an associated boundary control system. We fully characterize the cases in which the latter is impedance resp. scattering passive in terms of the associated trace operators. Furthermore, based on a non-standard factorization of $S$ we introduce an equivalence transform of $\mathcal{A}$ that maps the abstract second-order system (e.g., $\mathcal{A} = \left[\begin{smallmatrix} 0 & I \\ \Delta & -D \end{smallmatrix}\right]$ for the wave equation in position-momentum formulation) into widely-used alternative representation involving lower-order spatial derivatives on the jet space (i.e., $\left[\begin{smallmatrix} 0 & \nabla \\ \operatorname{div} & -D \end{smallmatrix}\right]$ corresponding to the wave equation in strain-momentum formulation). We illustrate the suggested approach on the example of a $n$-dimensional wave equation and a Maxwell equation.

math.AP↗

arXiv2025

Funnel control for passive infinite-dimensional systems

We consider funnel control for linear infinite-dimensional systems that are impedance passive, meaning that they satisfy an energy balance in which the stored energy equals the squared norm of the state and the supplied power is the inner product of input and output. For the analysis we employ the system node approach, which offers a unified framework for infinite-dimensional systems with boundary and distributed control and observation. The resulting closed-loop dynamics are governed by a nonlinear evolution equation; we establish its solvability and hence the applicability of funnel control to this class. The applicability is illustrated by an Euler-Bernoulli beam, which is studied in two distinct scenarios: once with boundary control and once with distributed control.

math.OC↗

arXiv2025

Weak solutions of port-Hamiltonian systems

We consider port-Hamiltonian systems from a geometric perspective, where the quantities involved such as state, flows, and efforts evolve in (possibly infinite-dimensional) Banach spaces. The main contribution of this article is the introduction of a weak solution concept. In this framework we show that the derivative of the state naturally lives in a space that, for ordinary evolution equations, plays the role of an extrapolation space. Through examples, we demonstrate that this approach is consistent with the weak solution framework commonly used for partial differential equations.

math.DS↗

arXiv2025

Modeling of radiating curved cables via coupled telegrapher's and Maxwell's equations

We investigate the electromagnetic interactions of cable harnesses in the time domain. We present a novel model that allows for curved cables, extending the standard assumptions typically made in transmission line modeling. The cables are described by the telegrapher's equations, the classical model for transmission lines, driven by input signals implemented through appropriate boundary conditions, such as imposed voltages at cable ends. The cables interact via electromagnetic radiation; the latter is determined by Maxwell's equations. This interaction is incorporated into the model through boundary conditions imposed on the electromagnetic field. The resulting coupling between the transmission lines and Maxwell's equations is energetically consistent. In particular, we show that the coupled system satisfies a global power balance.

math.AP↗

arXiv2025

Integrated Semigroups for abstract differential-algebraic equations

We study integrated semigroups for infinite-dimensional differential-algebraic equations (DAEs) admitting a resolvent index. Building on the notion of integrated semigroups for the abstract Cauchy problem $\frac{d}{d t}x=Ax$, we extend this concept to the DAE setting. The resulting framework is used to analyze inhomogeneous DAEs and plays a central role in characterizing their solutions.

math.FA↗

arXiv2025

The infinite-dimensional dissipation inequality

We study the dissipativity of linear infinite-dimensional systems with respect to a prescribed quadratic supply rate functional. We characterize this property via an operator inequality that also yields the system's dissipation rate. We also derive implications for the linear-quadratic optimal control problem on the nonnegative real half-line.

math.FA↗

arXiv2025

Port-Hamiltonian modeling of rigid multibody systems

We employ a port-Hamiltonian approach to model nonlinear rigid multibody systems subject to both position and velocity constraints. Our formulation accommodates Cartesian and redundant coordinates, respectively, and captures kinematic as well as gyroscopic effects. The resulting equations take the form of nonlinear differential-algebraic equations that inherently preserve an energy balance. We show that the proposed class is closed under interconnection, and we provide several examples to illustrate the theory.

math.DS↗

arXiv2024

The modulating function method for state estimation and feedback of infinite-dimensional systems

We investigate state feedback and observation for infinite-dimensional linear systems, including a variety of partial differential equations with boundary control and observation. We extend the modulating function approach to infinite-dimensional systems. This approach, simply put, involves reconstructing part of the state by convolving with null controls of the adjoint system. We show how this method aids in state reconstruction, and we also examine distributional solutions of the adjoint system, showing their ability to handle unbounded feedback operators. This enables us to use feedback from spatial point evaluations in partial differential equations.

math.OC↗

arXiv2024

Regularization and passivity-preserving model reduction of quasilinear magneto-quasistatic coupled problems

We consider the quasilinear magneto-quasistatic field equations that arise in the simulation of low-frequency electromagnetic devices coupled to electrical circuits. Spatial discretization of these equations on 3D domains using the finite element method results in a singular system of differential-algebraic equations (DAEs). First, we analyze the structural properties of this system and present a novel regularization approach based on projecting out the singular state components. Next, we explore the passivity of the variational magneto-quasistatic problem and its discretization by defining suitable storage functions. For model reduction of the magneto-quasistatic system, we employ the proper orthogonal decomposition (POD) technique combined with the discrete empirical interpolation method (DEIM), to facilitate efficient evaluation of the system's nonlinearities. Our model reduction approach involves the transformation of the regularized DAE into a system of ordinary differential equations, leveraging a special block structure inherent in the problem, followed by applying standard model reduction techniques to the transformed system. We prove that the POD-reduced model preserves passivity, and for the POD-DEIM-reduced model, we propose to enforce passivity by perturbing the output in a way that accounts for DEIM errors. Numerical experiments illustrate the effectiveness of the presented model reduction methods and the passivity enforcement technique.

math.NA↗

arXiv2024

Linear-quadratic optimal control for abstract differential-algebraic equations

In this paper, we extend a classical approach to linear quadratic (LQ) optimal control via Popov operators to abstract linear differential-algebraic equations (ADAEs) in Hilbert spaces. To ensure existence of solutions, we assume that the underlying differential-algebraic equation has index one in the pseudo-resolvent sense. This leads to the existence of a degenerate semigroup that can be used to define a Popov operator for our system. It is shown that under a suitable coercivity assumption for the Popov operator the optimal costs can be described by a bounded Riccati operator and that the optimal control input is of feedback form. Furthermore, we characterize exponential stability of ADAEs which is required to solve the infinite horizon LQ problem.

math.OC↗