Purpose – The purpose of this paper is to carry out a finite element simulation of a physically non-linear phase change problem in a two-dimensional space without adaptive remeshing or moving-mesh algorithms. The extended finite element method (XFEM) and the level set method (LSM) were used to capture the transient solution and motion of phase boundaries. It was crucial to consider the effects of unequal densities of the solid and liquid phases and the flow in the liquid region. Design/methodology/approach – The XFEM and the LSM are applied to solve non-linear transient problems with a phase change in a two-dimensional space. The model assumes thermo-dependent properties of the material and unequal densities of the phases; it also allows for convection in the liquid phase. A non-linear system of equations is derived and a numerical solution is proposed. The Newton-Raphson method is used to solve the problem and the LSM is applied to track the interface. Findings – The robustness and utility of the method are demonstrated on several two-dimensional benchmark problems. Originality/value – The novel procedure based on the XFEM and the LSM was developed to solve physically non-linear phase change problems with unequal densities of phases in a two-dimensional space.

Purpose -Of particular interest is the ability of the extended finite element method (XFEM) to capture transient solution and motion of phase boundaries without adaptive remeshing or moving-mesh algorithms for a physically nonlinear phase change problem. The paper aims to discuss this issue. Design/methodology/approach -The XFEM is applied to solve nonlinear transient problems with a phase change. Thermal conductivity and volumetric heat capacity are assumed to be dependent on temperature. The nonlinearities in the governing equations make it necessary to employ an effective iterative approach to solve the problem. The Newton-Raphson method is used and the incremental discrete XFEM equations are derived. Findings -The robustness and utility of the method are demonstrated on several one-dimensional benchmark problems. Originality/value -The novel procedure based on the XFEM is developed to solve physically nonlinear phase change problems.

The essential parameters for structure integrity assessment in Linear Elastic Fracture Mechanics (LEFM) are Stress Intensity Factors (SIFs). The estimation of SIFs can be done by analytical or numerical techniques. The analytical estimation of SIFs is limited to simple structures with non-complicated boundaries, loads and supports. An effective numerical technique for analyzing problems with singular fields, such as fracture mechanics problems, is the extended finite element method (XFEM).In the paper, XFEM is applied to compute an actual stress field in a twodimensional cracked body. The XFEM is based on the idea of enriching the approximation in the vicinity of the discontinuity. As a result, the numerical model consists of three types of elements: non-enriched elements, fully enriched elements (the domain of whom is cut by a discontinuity), and partially enriched elements (the so-called blending elements). In a blending element, some but not all of the nodes are enriched, which adds to the approximation parasitic term.The error caused by the parasitic terms is partly responsible for the degradation of the convergence rate. It also limits the accuracy of the method. Eliminating blending elements from approximation space and replacing them with standard elements, together with applying shifted-basis enrichment, makes it possible to avoid the problem. The numerical examples show improvements in results when compared with the standard XFEM approach.

Purpose: The objective of the work is to develop and implement the original concept of Repository of Didactic Processes Data (RDPD) for universities. The task of the Repository is to handle formally organised content in a digital form, covering resources created in connection with didactic processes, and the origin of which is a university community. These data should be: as complete as possible, available on the Internet at any time and easy to find and retrieve, stored in commonly used formats, contain a clear indication of the stored resources, without any costs for the user downloading them. Design/methodology/approach: The concept of the Repository was developed on the basis of the results of consultations with the academic community – its primary target audience. Comments from the representatives of the Repository future main users were taken into account. An analysis of the existing available repository systems in terms of their functionality, adaptability to the specificity of data, and popularity was carried out in order to select the solution that could be the foundation for RDPD. Then, the following tasks were undertaken in the environment of the selected system: adapting the data schema developed for RDPD, the implementation of the operations of loading, browsing, and searching of data, and user management. Findings: As a result of research and analyses, DSpace was proposed as the basis for the RDPD system. The logical metadata layers as well as the technical implementation of the proposed Repository in the DSpace system were elaborated. Practical implications: The implementation of the RDPD system may significantly facilitate and support the university management process. Originality/value: There are many initiatives regarding institutional repositories within the higher education sector. However, there is no institutional repository dedicated strictly to the storage and management of data generated by university educational processes. The developed repository is the solution to the problem. Keywords: institutional repository, data management, higher education didactic processes, software customisation, DSpace. Category of the paper: Conceptual paper, Case study.

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