Surface deformation. I

This article surveys results on the theory of deformation and infinitesimal deformation of surfaces in three-dimensional Euclidean space that have been obtained in the last 25–30 years and do not appear in previous survey articles.Translated from Itogi Nauki i Tekhniki Seriya Problemy Geometrii, Vol. 23, pp. 131–184, 1991.     

Surfaces in a pseudo-Euclidean space

A survey of results on regular and nonregular surfaces in a three-dimensional pseudo-Euclidean space. The method of approximating a convex surface by polyhedra and the intrinsic construction of polyhedra of negative curvature are considered in detail. A theorem on the existence in a pseudo-Euclidean space of a convex polyhedron with given polyhedral metric of negative curvature with a finite number of vertices is proved.Translated from Itogi Nauki i Tekhniki, Seriya Problemy Geometrii, Vol. 11, pp. 177–202, 1980.     

Dynamic shortest paths and transitive closure: Algorithmic techniques and data structures

In this paper, we survey fully dynamic algorithms for path problems on general directed graphs. In particular, we consider two fundamental problems: dynamic transitive closure and dynamic shortest paths. Although research on these problems spans over more than three decades, in the last couple of years many novel algorithmic techniques have been proposed. In this survey, we will make a special effort to abstract some combinatorial and algebraic properties, and some common data-structural tools that are at the base of those techniques. This will help us try to present some of the newest results in a unifying framework so that they can be better understood and deployed also by non-specialists.     

Free boundary problems for nonlinear evolution equations in metallurgy,medicine, and ecology

We study free boundary problems for an unknown scalar function and its level surfaces. Questions of uniqueness and existence of solutions are discussed. A survey of constructive methods of solution of particular problems and of mathematical prognostication in relevant areas of natural sciences is presented.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 1, pp. 67–76, January, 1992.     

Unique Determination of Locally Convex Surfaces with Boundary and Positive Curvature of Genus p ≥ 0

We prove the next result. If two isometric regular surfaces with regular boundaries, of an arbitrary finite genus, and positive Gaussian curvature in the three-dimensional Euclidean space, consist of two congruent arcs corresponding under the isometry (lying on the boundaries of these surfaces or inside these surfaces) then these surfaces are congruent.

     

Chaotic dynamics in three dimensions: A topological proof for a triopoly game model

We rigorously prove the existence of chaotic dynamics for a triopoly game model. In the model considered, the three firms are heterogeneous and in fact each of them adopts a different decisional mechanism, i.e., linear approximation, best response and gradient mechanisms, respectively. The method we employ is the so-called “Stretching Along the Paths” (SAP) technique, based on the Poincaré–Miranda Theorem and on the properties of the cutting surfaces.     

Games of Simple Pursuit and Approach on a Two-Dimensional Cone

The complete solution of two differential games with simple motion on a two-dimensional cone is presented. The method of generalized (singular) characteristics is used for the analysis of singular paths. The level lines of the game value and optimal phase portrait are constructed, and the latter is shown to include several types of singular surfaces (dispersal, equivocal, universal). An algorithm is developed for the construction of the synthesis for both players and is used in computer simulation.     

Surfaces of revolution in the Heisenberg group and the spectral generalization of the Willmore functional

We study the generalization of the Willmore functional for surfaces in the three-dimensional Heisenberg group. Its construction is based on the spectral theory of the Dirac operator entering into theWeierstrass representation of surfaces in this group. Using the surfaces of revolution we demonstrate that the generalization resembles the Willmore functional for the surfaces in the Euclidean space in many geometrical aspects. We also observe the relation of these functionals to the isoperimetric problem.     

Disjoint paths, planarizing cycles, and spanning walks

We study the existence of certain disjoint paths in planar graphs and generalize a theorem of Thomassen on planarizing cycles in surfaces. Results are used to prove that every 5-connected triangulation of a surface with sufficiently large representativity is hamiltonian, thus verifying a conjecture of Thomassen. We also obtain results about spanning walks in graphs embedded in a surface with large representativity.

     

Mathematical Statement of Boundary Conditions for Problems of Three-Dimensional Deformation of Plates

We consider the problem of mathematical statement of boundary conditions on the end surfaces of elastic plates for a model that describes three-dimensional deformation of these bodies. We show that there exist five conditions that have a certain physical meaning and characterize the conditions of fixation of a plate or loading on its end surfaces. We illustrate the results obtained for a circular plate rigidly fixed on its ends and loaded over the lateral surfaces.     

Graph surfaces of codimension two over three-dimensional Carnot–Carathéodory spaces

An area formula for graph surfaces of codimension two over three-dimensional Carnot–Carathéodory spaces is derived and applied to obtain basic properties of minimal surfaces.     

Operator splitting for the numerical solution of free surface flow at low capillary numbers

Free surface flows are pervasive in engineering and biomedical applications. In many interesting cases—particularly when small length scales are involved—surface forces (capillarity) dominate the flow dynamics. In these cases, computing the flow together with the shape of the surfaces, requires specialized solution techniques. This article investigates the capabilities of an operator splitting/finite elements method at handling accurately incompressible viscous flow with free surfaces at low capillary numbers. The test case of flow in the downstream section of a slot coater is used for three reasons: (1) it is an established benchmark; (2) it represents an idealized, yet industrially relevant flow; (3) high-fidelity results obtained with monolithic algorithms are available in literature. The flow and free surface shape attained with the new operator splitting scheme agree very satisfactorily with the results obtained with monolithic solvers. Because of its inherent computational simplicity, the new operator splitting scheme is attractive for large-scale simulations, three-dimensional flows, and flows of complex fluids.     

Metric aspects of conic surfaces

We give a survey on various results regarding the metric aspects of conic surfaces with emphasis on the prescribing curvature problem for conic surfaces.     

Surfaces in the lightlike cone

In this paper, we study surfaces in the lightlike cone. We first obtain fundamental formulas for surfaces in a lightlike cone of general dimensions and then characterize certain homogeneous surfaces in the three-dimensional lightlike cone and four-dimensional lightlike cone, respectively.     

Soap-film-like minimal surfaces spanning knots

It is proved that any three-times continuously differentiable, nontrivial knot in three-dimensional euclidean space supports a surface that minimizes area among nearby surfaces but that does not touch all of the supporting knot. This provides a mathematical model of a physical phenomenon occurring in soap-films. The notion of a homotopically spanning surface is defined to determine an appropriate class of admissible surfaces, and it is shown that there is a lower bound on the area of admissible surfaces. The existence of an area minimizing admissible surface is then proved by the direct method based on earlier work of E. R. Reiffenberg.     

Invariants of knots,surfaces in R<Superscript>3</Superscript>, and foliations

We give a survey of some known results related to combinatorial and geometric properties of finite-order invariants of knots in a three-dimensional space. We study the relationship between Vassiliev invariants and some classical numerical invariants of knots and point out the role of surfaces in the investigation of these invariants. We also consider combinatorial and geometric properties of essential tori in standard position in closed braid complements by using the braid foliation technique developed by Birman, Menasco, and other authors. We study the reductions of link diagrams in the context of finding the braid index of links. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 9, pp. 1239–1252, September, 2007.     

A version of Turán’s problem for positive definite functions of several variables

We present a systematic approach to solving the problem of affine homogeneity of real hypersurfaces in the three-dimensional complex space. This question is an important part of the general problem of holomorphic classification of homogeneous real hypersurfaces in three-dimensional complex spaces. In contrast to the two-dimensional case, the whole problem (just as its affine part) has not yet been fully studied, although there exist a large number of examples of homogeneous manifolds. We study only the class of tubular type surfaces, which is defined by conditions imposed on the 2-jet of their canonical equations and generalizes the class of tube manifolds. We discuss the procedure of describing all matrix Lie algebras corresponding to the homogeneous manifolds under consideration. In the class that we study, we distinguish four cases depending on the third-order Taylor coefficients of the canonical equations; in three of these cases, the Lie algebras and the corresponding affine homogeneous surfaces are completely described. The key point of the proposed approach is the solution of a large system of quadratic equations that corresponds to each of the homogeneous surfaces.     

Direct method for the design of optimal three-dimensional aerodynamic shapes

A direct optimization method for a broad class of three-dimensional aerodynamic shapes based on the approximation of the desired geometry by Bernstein-Bézier surfaces is developed. The high efficiency of the method is demonstrated by applying it to the design of an optimal supersonic section of an axisymmetric maximum-thrust de Laval nozzle. The method is also tested as applied to the design of a three-dimensional supersonic nozzle section in a dense multi-nozzle setup. In addition to three-dimensional supersonic nozzle sections with a circular throat, nozzles with a varying throat shape are considered. The results suggest that the method can be applied to various problems of 3D shape optimization.     

Classical motions of infinitesimal rotators on Mylar balloons

This paper starts with the derivation of the most general equations of motion for the infinitesimal rotators moving on arbitrary two-dimensional surfaces of revolution. Both geodesic and geodetic (i.e., without any external potential) equations of motion on surfaces with nontrivial curvatures that are embedded into the three-dimensional Euclidean space are discussed. The Mylar balloon as a concrete example for the application of the scheme was chosen. A new parameterization of this surface is presented, and the corresponding equations of motion for geodesics and geodetics are expressed in an analytical form through the elliptic functions and elliptic integrals. The so-obtained results are also compared with those for the two-dimensional sphere embedded into the three-dimensional Euclidean space for which it can be shown that the geodesics and geodetics are plane curves realized as the great and small circles on the sphere, respectively.     

Index iteration theory for symplectic paths and multiple periodic solution orbits

In this paper, a survey on the index iteration theory for symplectic paths is given. Three applications of this theory are presented including closed characteristics on convex hypersurfaces and brake orbits on bounded domains.