arXiv subjects

Andrey P. Jivkov

Publications and source records attributed to Andrey P. Jivkov.

6 recordsLinked to original sources

arXiv2026

Incidence-based Combinatorial Geometry on Cell Complexes

Combinatorial Mesh Calculus (CMC) formulates conservation laws directly on cell complexes using combinatorial differential forms and their cochain representations. This note develops an incidence-based geometric extension of that framework for directional quantities and local geometric structure on explicit cellular organisation. The central construction is a family of local fibres generated intrinsically by the incidence structure of the complex. Each vertex carries a vector space spanned by its incident edge directions, providing a combinatorial analogue of a tangent space whose dimension reflects local topology. These fibres define local coefficient spaces for incidence-based vector-, covector- and endomorphism-valued cochains. Directed transport maps compare states attached to neighbouring fibres, while a canonical solder form relates fibre directions to the underlying cell-complex structure. Together they give rise to finite combinatorial analogues of transport, torsion, curvature and metric structure. Evaluation cup products provide pairings between kinematic and force-like quantities, while bundle Hodge operators induced by the fibre metric relate vector- and covector-valued cochains, and weighted covariant incidence operators define degree-raising transport-corrected operations on incidence cochains. The framework does not assume a smooth manifold, fixed-rank bundle, cellular sheaf or local system. Instead, geometric structure is generated directly from the organisation represented by the cell complex. The resulting theory establishes a combinatorial scaffold for geometry on explicit cellular organisation and identifies the principal mathematical questions required for its further development, including admissible transport classes, metric compatibility, Cartan-type structure equations and locality-dependent algebraic structures.

math.GM↗

arXiv2026

Variational formulations of transport phenomena on combinatorial meshes

We develop primal and mixed variational formulations of transport phenomena on cell complexes with simple polytope connectivity. This framework addresses materials with internal structures comprising components of different topological dimensions, where cells of each dimension may possess distinct physical properties. The approach, which we call Combinatorial Mesh Calculus (CMC), extends Forman's combinatorial differential forms, previously used to formulate strong conservation laws. CMC operates directly on meshes without requiring smooth embeddings, using discrete analogues of the exterior derivative, Hodge star, and co-differential operators. Our mixed formulation leads to a block-diagonal mass-like matrix arising from inner products weighted by material coefficients, enabling efficient local elimination strategies within the mixed system. CMC differs from Discrete Exterior Calculus, which requires circumcentric duality and well-centred meshes, and from Finite Element Exterior Calculus, which constructs polynomial spaces on smooth domains. Our framework applies to general cell complexes, including curved cells and irregular meshes; nonetheless irregularity leads to worse numerical performance. The mathematical development proceeds in parallel between the smooth and discrete settings, establishing correspondences between continuous and discrete operators. Initial boundary value problems are formulated for mass diffusion, heat conduction, charge transport, and fluid flow through porous media. Numerical examples on regular and irregular meshes in two and three dimensions demonstrate agreement with analytical solutions. The framework enables modelling of transport in materials where microstructural topology influences macroscopic behaviour, with applications to polycrystalline materials, composites, and porous media.

math-ph↗

arXiv2025

Plastic deformation as a phase transition: a combinatorial model of plastic flow in copper single crystals

Continuum models of plasticity fail to capture the richness of microstructural evolution because the continuum is a homogeneous construction. The present study shows that an alternative way is available at the mesoscale in the form of truly discrete constructions and in the discrete exterior calculus. A pre-existing continuum mean-field model with two parameters is rewritten in the language of the latter to model the properties of a network of plastic slip events in a perfect copper single crystal under uniaxial tension. The behaviour of the system is simulated in a triangular 2D mesh in 3D space employing a Metropolis-Hastings algorithm. Phases of distinct character emerge and both first-order and second-order phase transitions are observed. The phases represent arrangements of the plastic slip network with different combinations of collinear, coplanar, non-collinear and non-coplanar active slip systems. Furthermore, some of these phases can be interpreted as representing crystallographic phenomena like activation of secondary slip systems, strain localisation and fracture or amorphisation. The first-order transitions mostly occur as functions of the applied stress, while the second-order transitions occur exclusively as functions of the mean-field coupling parameter. The former are reminiscent of transitions in other statistical-mechanical models, while the latter find parallels in experimental observations.

cond-mat.mtrl-sci↗

arXiv2025

Calculus with combinatorial differential forms for fluid flow analysis in porous and fractured media

The fabric of porous and fractured media contains solid regions (grains) and voids. The space conducting fluids is a system of connected voids with variable geometries. Relative to the grain sizes, the voids can be voluminous with three comparable large extensions, narrow expansive with two comparable large extensions and one smaller extension, and thin long with one comparable large extension and two smaller extensions. The widely used representation of void spaces by systems of spheres connected by cylinders (pore network models) is an acceptable approximation for some special cases, but not for most porous and fractured media. We propose a flexible method for modelling such media by mapping their measured fabric's characteristics - void and grain volume distributions and shapes - onto polyhedral tessellations of space. The map assigns voluminous voids and grains to polyhedrons (3D), narrow expansive voids to some polyhedral faces (2D), and thin long voids to some polyhedral edges (1D), as dictated by experimental data. The analysis of transport through such discrete structures with components of different dimensions is performed by a novel mathematical method, which uses combinatorial differential forms to represent physical properties and their fluxes, as well as structure-preserving operators on such forms to formulate the conservation laws exactly and directly in matrix form, ready for computation. The method allows for individual material properties, such as conductivity, to be assigned to voids of all dimensions, so that the three types of voids are suitably represented. Publicly available XCT images of four different rocks are used to test the method.

math-ph↗

arXiv2024

Kinetic view on dynamic plasticity of crystalline solids

Microstructural changes in solids, driven by energy flows, do not develop in a static continuous space, such as the space considered in conventional plasticity models. The applied forces create an evolving internal energy landscape, which is constrained by crystallography but has characteristic spatial and temporal scales that form dynamically. To describe this view, we replace a common model for the evolution of dislocation substructure in metals with the evolution of microscopic slips in a combinatorial structure referred to as a polytopal cell complex (PCC). The micro-slips are associated with the 2-cells (faces) of the PCC and are driven by the minimisation of a properly defined Lagrangian. The approach provides a comprehensive statistical and thermodynamic description of plastic flow development. It allows the investigation of energy levels associated with different slip systems and reveals the microscopic mechanisms that result in the phenomenon of strain rate sensitivity.

cond-mat.mtrl-sci↗

arXiv2022

Diffusion in multi-dimensional solids using Forman's combinatorial differential forms

The formulation of combinatorial differential forms, proposed by Forman for analysis of topological properties of discrete complexes, is extended by defining the operators required for analysis of physical processes dependent on scalar variables. The resulting description is intrinsic, different from the approach known as Discrete Exterior Calculus, because it does not assume the existence of smooth vector fields and forms extrinsic to the discrete complex. In addition, the proposed formulation provides a significant new modelling capability: physical processes may be set to operate differently on cells with different dimensions within a complex. An application of the new method to the heat/diffusion equation is presented to demonstrate how it captures the effect of changing properties of microstructural elements on the macroscopic behavior. The proposed method is applicable to a range of physical problems, including heat, mass and charge diffusion, and flow through porous media.

math-ph↗