Fluid-Structure Interactions: Control and Optimization

We focus on fluid-structure interactions (FSI) described by incompressible, viscous fluids coupled with elastic structures that move and deform inside them. Fluid-structure interactions have various medical and engineering applications, ranging from blood flow in stenosed arteries to the design of small-scale unmanned aircrafts. In most of the applications, the goal is the optimization or optimal control of the considered process. Specific examples include: minimizing turbulence, achieving given targets for fluid velocity or pressure, and minimizing the hydro-elastic pressure on the interface between the two environments. Therefore we consider PDE-constrained optimization and optimal control problems governed by moving boundary fluid-elasticity interactions. These interactions are highly nonlinear couplings of parabolic-hyperbolic type, described by a mismatch of regularity of the two solutions at the common interface. We discuss main challenges and describe the results that we obtained so far regarding the existence of optimal controls and the derivation of necessary optimality conditions

The role of structural viscoelasticity in deformable porous media with incompressible constituents: applications in biomechanics

The main goal of this work is to clarify and quantify, by means of mathematical analysis, the role of structural viscoelasticity in the biomechanical response of deformable porous media with incompressible constituents to sudden changes in external applied loads. Models of deformable porous media with incompressible constituents are often utilized to describe the behavior of biological tissues, such as cartilages, bones and engineered tissue scaffolds, where viscoelastic properties may change with age, disease or by design. Here, for the first time, we show that the fluid velocity within the medium could increase tremendously, even up to infinity, should the external applied load experience sudden changes in time and the structural viscoelasticity be too small. In particular, we consider a one-dimensional poro-visco-elastic model for which we derive explicit solutions in the cases where the external applied load is characterized by a step pulse or a trapezoidal pulse in time. By means of dimensional analysis, we identify some dimensionless parameters that can aid the design of structural properties and/or experimental conditions as to ensure that the fluid velocity within the medium remains bounded below a certain given threshold, thereby preventing potential tissue damage. The application to confined compression tests for biological tissues is discussed in detail. Interestingly, the loss of viscoelastic tissue properties has been associated with various disease conditions, such as atherosclerosis, Alzheimer's disease and glaucoma. Thus, the findings of this work may be relevant to many applications in biology and medicine

Local Hadamard well-posedness for nonlinear wave equations with supercritical sources and damping

AbstractWe consider the wave equation with supercritical interior and boundary sources and damping terms. The main result of the paper is local Hadamard well-posedness of finite energy (weak) solutions. The results obtained: (1) extend the existence results previously obtained in the literature (by allowing more singular sources); (2) show that the corresponding solutions satisfy Hadamard well-posedness conditions during the time of existence. This result provides a positive answer to an open question in the area and it allows for the construction of a strongly continuous semigroup representing the dynamics governed by the wave equation with supercritical sources and damping

Analysis of nonlinear poro-elastic and poro-visco-elastic models

We consider the initial and boundary value problem for a system of partial differential equations describing the motion of a fluid–solid mixture under the assumption of full saturation. The ability of the fluid phase to flow within the solid skeleton is described by the permeability tensor, which is assumed here to be a multiple of the identity and to depend nonlinearly on the volumetric solid strain. In particular, we study the problem of the existence of weak solutions in bounded domains, accounting for non-zero volumetric and boundary forcing terms. We investigate the influence of viscoelasticity on the solution functional setting and on the regularity requirements for the forcing terms. The theoretical analysis shows that different time regularity requirements are needed for the volumetric source of linear momentum and the boundary source of traction depending on whether or not viscoelasticity is present. The theoretical results are further investigated via numerical simulations based on a novel dual mixed hybridized finite element discretization. When the data are sufficiently regular, the simulations show that the solutions satisfy the energy estimates predicted by the theoretical analysis. Interestingly, the simulations also show that, in the purely elastic case, the Darcy velocity and the related fluid energy might become unbounded if indeed the data do not enjoy the time regularity required by the theory

PRIORITETI UPRAVLJANJA JAVNIM KOMUNALNIM USLUGAMA U ZAPADNOJ RUMUNJSKOJ

Public utility services are an important vector for the development of regional and local communities. Providing these services is equally important to citizens, central, regional and local authorities, and academics. The management of public utility services needs to be completed in the spirit of an efficient and performant process. This paper highlights the perception of the users of public utility services regarding the quality of various public services. Also, it identifies potential improvement measures that can be adopted by the authorities with competences in the field of utility services. In this respect, we apply a methodology based on the survey method, considering a sample of 220 respondents, between December 2014 and April 2015 at the level of the Western Region of Romania, namely the counties of Timis, Caras-Severin, Arad and Hunedoara. The main conclusion of the study reveals users’ dissatisfaction with the quality of public utility services provision, as well as the lack of communication between authorities and citizens.The results of the present paper can form a basis for well-grounded proposals for efficient measures which need to be implemented by local and regional authorities in order to improve the provision of public utility services.Javne komunalne usluge važan su vektor razvoja regionalnih i lokalnih zajednica. Te usluge jednako su važne građanima, središnjim, regionalnim i lokalnim vlastima, ali i akademskoj zajednici. Upravljanje javnim komunalnim uslugama mora biti učinkovit i djelotvoran proces. Ovaj rad bavi se percepcijom kvalitete javnih komunalnih usluga od strane njihovih korisnika. Također navodi moguće mjere za poboljšanje tih usluga koje mogu uvesti tijela nadležna za upravljanje komunalnim uslugama. U radu se koristi metoda ankete te se analizira uzorak odgovora 220 ispitanika prikupljenih u razdoblju od prosinca 2014. do travnja 2015. u zapadnoj Rumunjskoj, točnije u općinama Timis, Caras-Severin, Arad i Hunedoara. Zaključak studije otkriva nezadovoljstvo korisnika kvalitetom pružanja javnih komunalnih usluga, ali i nedostatak komunikacije između nadležnih tijela i građana. Rezultati ovog rada mogu biti temelj za predlaganje mjera koje lokalne i regionalne vlasti mogu provesti kako bi poboljšale kvalitetu komunalnih usluga

DIFFICULTIES CONCERNING PUBLIC SECTOR EFFICIENCY AND PERFORMANCE MEASUREMENT

The ability to measure public sector performance is a necessity for policymakers as well as academics and citizens of a country. This article aims to identify ways of measuring public sector performance using the measurement applicable to all countries and outlining opportunities for comparability among them. Thus, the authors highlight opportunities for performance measurement and public sector efficiency using various methods of non-parametric and parametric analysis. The starting point of the analysis considers the concept of performance, encompasses the proposed terms of productivity, efficiency and effectiveness; therefore, the measurement of public sector performance requires an exhaustive analysis in multidimensional terms, covering all core areas of a country. Moreover, understanding and developing robust international comparison possibilities will give in practice a structural framework for measuring the performance of particular relevance. Study findings indicate that performance measurement and implicitly public sector efficiency is a complex and difficult task that goes beyond simply measuring of productivity and efficiency, and requires aggregation of several key areas related to the results of a state. In summary, the analysis framework of the performance and efficiency of public sector is outlined both in terms of relevance of indicators and the methodology used. It demonstrates that methods of non-parametric analysis work at their best when all aspects of the production process can be captured in a limited number of input and output dimensions.KEYWORDS: performance, efficiency, public sector, non-parametric methods, parametric methods