Lab

Parallel and Distributed Systems Laboratory

About the lab

The Parallel and Distributed Systems Laboratory is focusing on parallelization of algorithms and their efficient implementation on parallel and distributed computers, with the emphasis on modelling and simulating complex systems and processes in the fields of Chemistry, Biology and Medicine.

Lab web page:
http://e6.ijs.si/ParallelAndDistributedSystems

Featured projects (9)

Project
Develop a fast scalable easy-to-use library for solving PDEs with meshless methods. https://e6.ijs.si/ParallelAndDistributedSystems/products/medusa/ Our team started the development of Medusa library in 2015 to support our research in the field of numerical analysis and to ease implementation of applied projects. Over time, the interface grew and matured, putting emphasis on modularity, extensibility and reusability. Similarly to many open-source FEM libraries, it relies heavily on the C++ template system and allows the programs to be written independently of the number of spatial dimensions with negligible run-time and memory overhead. Special care is also taken to increase expressiveness and to be able to explicitly translate mathematical notation into program source code. However, source code is still standard compliant C++, which allows the user to use entirety of the C++ ecosystem. The open-source nature of the library is a novelty compared to the other libraries. We already utilized Medusa library for solving broad spectra of problems ranging from pure academic experiments like high order solutions of Poisson’s equation in 2D, 3D, and 4D, to applied thermo-fluid and thermo-elastic simulations of real life problems.
Project
DiTeR is a modular dynamic thermal rating (DTR) software designed to predict the thermal state of power lines in given operating and weather conditions. It can be used as a stand-alone program, via an online interface enabling the use of meteorological data, or as a part of operative system. Besides the thermal state, it can predict the maximum load allowed in given weather conditions and, for a given overload situation, the time till overheat. In 2019, we successfully completed tests required for its transfer to operational use, and successfully deployed DiTeR to operational use for 27 transmission lines in the Slovenian power network. In 2019, we also deployed DiTeR pilot into the Croatian transmission network. DiTeR is since 2020 marketed on the world-wide market by company Operato, a member of the ELES Group. The core of the DiTeR is a physical model for the simulation of heat transfer within the transmission power line under realistic weather conditions, where ambient temperature, wind velocity, rain rate, humidity, pressure and solar irradiance are considered as major factors of influence. DiTeR comprises the heat transport through the power line, heat generation by Joule heating and heat exchange with surrounding via convection, solar heating, radiation, rain impinging and evaporation. The DiTeR problem can be stated as the problem of heat transport with non-linear boundary conditions describing different heat terms due to the weather conditions. Although DiTeR can run in as a standalone software, it is targeted to primarily run as an embedded system within the SUMO framework, a heterogeneous collection of subsystem from different vendors that was developed to increase safety and security as well as the capacity of the existing transmission network. Its core is the integration platform, SUMO BUS, which is an enterprise integration bus, used for orchestrating the subsystems and facilitating data exchange between them. The communication between SUMO BUS and the subsystems is based on web services. More precisely, subsystems communicate with the bus via SOAP/HTTP interfaces. The purpose of DiTeR is to provide time evolution of thermal state of the power line with respect to the operational conditions and weather conditions. However, this simulation can be also used to predict operational safety limits. For each time step DiTeR runs nested simulation and computes the maximal current at which power line will not surpass safety limit assuming stationary weather conditions, referred also to as a thermal current. Besides thermal current DiTeR computes also the maximal time the power line can be safely utilized with higher current than thermal current, referred also to as time to overheat. Back end is the executable, that calculates DTR from user or machine provided input parameters. It is written in C++14 and can be compiled with GCC toolchain. https://e6.ijs.si/ParallelAndDistributedSystems/products/diter/
Project
System for mobile monitoring of vital physiological parameters and environmental context. In the center of the system is a wireless multi functional body sensor dimensions: 2x9cm, weight: 14 g) with two electrodes at the distance of 8 cm. The device primarily measures differential surface potential (ECG) between the proximal electrodes. The sensor has a long utonomy (up to 7 days), a low power wireless connection (BT4) to a Smartphone or other personal device (PDA), and corresponding software for standard interpretation of measurements. The software includes: - MobECG - a mobile application installed on the PDA. Its main functionalities include: establishing communication between the Savvy sensor and the PDA, visualization of the ongoing measurement, storing the measured data on the PDA storage, interaction with the user, and transferring the measurements to a secure storage server or Cloud platform. - VisECG - stand-alone software for visualization and basic analysis of the measured ECG on a safe storage server. The moderate resolution ECG is suitable for long-term personal cardiac activity monitoring, as well as for clinical use. Its exceptionally lightweight design allows for unobstructed use also during sports activities or during exhaustive physical work. Besides ECG, other features can be extracted from the measured potential, such as muscle activity and respiration. The sensor can also detect information about the measurement conditions such as movement and temperature, thus providing information that allows for ambient intelligence. The device can support solutions to every-day problems of the medical personal in hospitals, health clinics, homes for the elderly and health resorts. A commercial version of the medically certified ECG sensor – trademarked SAVVY ECG (www.savvy.si) – is available on the market since 2016.
Project
In February 2014 a severe icing storm hit Slovenia, and caused damage in order of 8.5 million € only on the power transmission network. In cooperation with Milan Vidmar Electric Power Research Institute (EIMV) and Slovenian Environment Agency (SEA) we developed and validated a DTRi model (Dynamic Thermal Rating - icing), which was implemented as a prototype system for operative forecasting and prevention of icing on high voltage transmission lines. We have validated the prototype system with measurements on an experimental site and through reconstruction of two real cases, on 1.2.2014 and 5.1.2016 on Beričevo-Divača line. The results of the study are promising, and therefore the customer decided to promote the system into the operative SUMO environment. For this purpose we also obtained additional founding from EU FP7 TETRACOM project. Both projects are led by members of our program group, while the customer is the company ELES. https://e6.ijs.si/ParallelAndDistributedSystems/projects/eles_icing/

Featured research (34)

Plasticity is a branch of solid mechanics, which deals with materials that upon sufficient deformation do not return to their original shape once the deforming force is released.Several plasticity models describing the yield condition exist, e.g. von Mises, Tresca, etc. Plasticity problems are usually solved by assuming an elastic deformation under the applied load, and correcting the stress-strain field iteratively, should the local yield criterion be violated. Traditionally the finite element method (FEM) is the numerical tool of choice for engineers who are solving such problems. In this work, however, we present the implementation of the von Mises plasticity model with non-linear isotropic hardening in our in-house developed MEDUSA library, utilizing radial basis function-generated finite differences (RBF-FD), which is beneficial compared to FEM, as it does not require a meshing step to discretize the domain. We define a simple plane stress case, where a 2D block is fixed at one edge, and a tensile force, which causes the block to deform, is applied to it at the opposite edge. Results are in good agreement with solutions obtained by Abaqus FEA, a commercial FEM solver.
The purpose of the present paper is development of an efficient meshless solution of steady incompressible Stokes flow problems with constant viscosity in two dimensions, with algebraic order of accuracy. This is achieved by employing a weak formulation with divergence-free matrix-valued quadratic Matérn (QM) radial basis function (RBF) for the shape function and divergence-free matrix-valued compactly supported Gaussian (CSG) RBF for the weight function on the computational domain and its boundary. The continuity equation is inherently built-in in the formulation and the pressure is eliminated from the formulation with the aid of divergence theorem and the choice of divergence-free weight function. The developed method is thus iteration free, and results in a banded system of equations to be solved jointly for both velocity components. Gauss–Legendre cell integration is performed in the current investigation. The characteristics of the method are assessed by changing its free parameters, i.e., weight functions’ sub-domain radius and shape functions’ support domain radius and the shape parameter. A sensitivity test for several choices of shape functions with regular centers arrangement is done to identify the appropriate support size for the shape and weight functions and stagnation errors are reported accordingly. To the best of our knowledge, this article is initiative in introducing the application of divergence-free MLPG method to incompressible flows, aiming at elimination of pressure from the governing equations in primitive variables, with the aid of divergence-free RBFs through weak formulation. Only the momentum equation needs to be solved. Hence, the formulation of the problem is much simpler than the building of divergence-free elements in the related mesh-based methods.
The popularity of local meshless methods in the field of numerical simulations has increased greatly in recent years. This is mainly due to the fact that they can operate on scattered nodes and that they allow a direct control over the approximation order and basis functions. In this paper we analyse two popular variants of local strong form meshless methods, namely the radial basis function-generated finite differences (RBF-FD) using polyharmonic splines (PHS) augmented with monomials, and the weighted least squares (WLS) approach using only monomials-a method also known as Diffuse Approximation Method. Our analysis focuses on the accuracy and stability of the numerical solution computed on scattered nodes in a two-and three-dimensional domain. We show that while the WLS variant is a better choice when lower order approximations are sufficient , the RBF-FD variant exhibits a more stable behavior and a higher accuracy of the numerical solution for higher order approximations, but at the cost of higher computational complexity.
The grain envelope model (GEM) describes the growth of envelopes of dendritic crystal grains during solidification. Numerically the growing envelopes are usually tracked using an interface capturing method employing a phase field equation on a fixed grid. Such an approach describes the envelope as a diffuse interface, which can lead to numerical artefacts that are possibly detrimental. In this work, we present a sharp-interface formulation of the GEM that eliminates such artefacts and can thus track the envelope with high accuracy. The new formulation uses an adaptive meshless discretization method to solve the diffusion in the liquid around the grains. We use the ability of the meshless method to operate on scattered nodes to accurately describe the interface, i.e., the envelope. The proposed algorithm combines parametric surface reconstruction, meshless discretization of parametric surfaces, global solution construction procedure and partial differential operator approximation using monomials as basis functions. The approach is demonstrated on a two-dimensional h-adaptive solution of diffusive growth of dendrites and assessed by comparison to a conventional diffuse-interface fixed-grid GEM.
In this paper, we present a novel parallel dimension-independent node positioning algorithm that is capable of generating nodes with variable density, suitable for mesh-less numerical analysis. A very efficient sequential algorithm based on Poisson disc sampling is parallelized for use on shared-memory computers, such as the modern workstations with multi-core processors. The parallel algorithm uses a global spatial indexing method with its data divided into two levels, which allows for an efficient multi-threaded implementation. The addition of bootstrapping enables the algorithm to use any number of parallel threads while remaining as general as its sequential variant. We demonstrate the algorithm performance on six complex 2-and 3-dimensional domains, which are either of non rectangular shape or have varying nodal spacing or both. We perform a run-time analysis of the algorithm, to demonstrate its ability to reach high speedups regardless of the domain and to show how well it scales on the experimental hardware with 16 processor cores. We also analyse the algorithm in terms of the effects of domain shape, quality of point placement, and various parallelization overheads.

Lab head

Gregor Kosec
Department
  • Department of Communication Systems
About Gregor Kosec
  • I am a principal investigator at Parallel and Distributed Systems Laboratory, Department E6, Jožef Stefan Institute, mostly dealing with computational modelling, adaptive meshless numerical analysis and parallel computing.

Members (10)

Matjaž Depolli
  • Jožef Stefan Institute
Aleksandra Rashkovska
  • Jožef Stefan Institute
Mitja Jančič
  • Jožef Stefan Institute
Filip Strniša
  • Jožef Stefan Institute
Miha Mohorčič
  • Jožef Stefan Institute
Urban Duh
  • Jožef Stefan Institute
Miha Rot
  • Jožef Stefan Institute
Viktor Cvrtila
  • Jožef Stefan Institute

Alumni (4)

Roman Trobec
  • Jožef Stefan Institute
Viktor Avbelj
  • Jožef Stefan Institute
Monika Kapus-Kolar
  • Jožef Stefan Institute
Jure Slak
  • Jožef Stefan Institute