D. Durban – författare

The optimal control of flexible structures is an active area of research. The main body of work in this area is concerned with the control of time-dependent displacements and stresses, and assumes linear elastic conditions, namely linear elastic material behavior and small defor- tion. See, e. g. , [1]–[3], the collections of papers [4, 5], and references therein. On the other hand, in the present paper we consider the static optimal control of a structure made of a nonlinear elastic material and und- going large deformation. An important application is the suppression of static or quasi-static elastic deformation in flexible space structures such as parts of satellites by the use of control loads [6]. Solar rad- tion and radiation from other sources induce a temperature field in the structure, which in turn generates an elastic displacement field. The displacements must usually satisfy certain limitations dictated by the allowed working conditions of various orientation-sensitive instruments and antennas in the space vehicle. For example, a parabolic reflector may cease to be effective when undergoing large deflection. The elastic deformation can be reduced by use of control loads, which may be imp- mented via mechanically-based actuators or more modern piezoelectric devices. When the structure under consideration is made of a rubb- like material and is undergoing large deformation, nonlinear material and geometric effects must be taken into account in the analysis.

This volume is a collection of the main lectures over a broad spectrum of rheological models with singularities as the "Leitmotiv", with 30 papers on the most recent developments in the analysis and understanding of non-linear singularities. Singularity-dominated local fields are frequently encountered in various branches of continuum mechanics, such as elasticity, plasticity, Newtonian fluids and more complex rheological models. Examples are provided by near tip fields of cracks, notches and wedges; interfacial phenomena; flow around corners, wedges and cones; moving contact lines in multiphase systems; cusps in fluid interfaces and shocks and localizations. The volume should be of interest to researchers and engineers in virtually all branches of continuum mechanics.

The optimal control of flexible structures is an active area of research. The main body of work in this area is concerned with the control of time-dependent displacements and stresses, and assumes linear elastic conditions, namely linear elastic material behavior and small defor- tion. See, e. g. , [1]–[3], the collections of papers [4, 5], and references therein. On the other hand, in the present paper we consider the static optimal control of a structure made of a nonlinear elastic material and und- going large deformation. An important application is the suppression of static or quasi-static elastic deformation in flexible space structures such as parts of satellites by the use of control loads [6]. Solar rad- tion and radiation from other sources induce a temperature field in the structure, which in turn generates an elastic displacement field. The displacements must usually satisfy certain limitations dictated by the allowed working conditions of various orientation-sensitive instruments and antennas in the space vehicle. For example, a parabolic reflector may cease to be effective when undergoing large deflection. The elastic deformation can be reduced by use of control loads, which may be imp- mented via mechanically-based actuators or more modern piezoelectric devices. When the structure under consideration is made of a rubb- like material and is undergoing large deformation, nonlinear material and geometric effects must be taken into account in the analysis.

The IUTAM Symposium on "Non-Linear Singularities in Defonnation and Flow" took place from March 17 to 21, 1997, at the Technion in Haifa, Israel, with 70 participants from 12 countries. The leitmotif of this Symposium brought together scientists working on singularity-dominated local fields in various branches of continuum mechanics, covering traditional solid and liquid behaviour as well as that of more complex non-linear materials; non-linearities arise either from the constitutive equations for the material or from the presence of interfaces or both. The scientific committee invited speakers who presented 34 papers in 12 sessions. Topics covered in the lectures included near tip fields of cracks, notches and wedges; flow around comers, wedges and cones; interfacial phenomena; moving contact lines in multiphase systems; cusps in fluid interfaces and shocks and localization. There was a general consensus among the participants that singularities induced by non-linearities provide a challenging and currently important area of research in mechanics, engineering and applied mathematics. Presentation and discussions during the symposium initiated further studies of problems in these interesting areas. This volume contains 30 full length papers, submitted by the lecturers after the symposium and reviewed to the standards of international scientific periodicals. It is our pleasure to acknowledge the efficient and tireless help of Mrs. Alice Goodman and Mr. Gideon Wachsman of the Faculty of Aerospace Engineering at the Technion. David Durban Anthony Pearson Haifa Cambridge April 1998 IX International Scientific Committee C. Atkinson (UK) G. I. Barenblatt (USA) H. -c.