Performance Evaluation of Parallel Haemodynamic Computations on Heterogeneous Clouds

The article presents performance evaluation of parallel haemodynamic flow computations on heterogeneous resources of the OpenStack cloud infrastructure. The main focus is on the parallel performance analysis, energy consumption and virtualization overhead of the developed software service based on ANSYS Fluent platform which runs on Docker containers of the private university cloud. The haemodynamic aortic valve flow described by incompressible Navier-Stokes equations is considered as a target application of the hosted cloud infrastructure. The parallel performance of the developed software service is assessed measuring the parallel speedup of computations carried out on virtualized heterogeneous resources. The performance measured on Docker containers is compared with that obtained by using the native hardware. The alternative solution algorithms are explored in terms of the parallel performance and power consumption. The investigation of a trade-off between the computing speed and the consumed energy is performed by using Pareto front analysis and a linear scalarization method

Sensitivity of dynamic behaviour of the FE model: Case study for the ignalina NPP reactor building

The 3D thin‐walled finite element model of Ignalina NPP Unit 2 reactor building was developed aimed at the evaluation of the global dynamic behaviour with a focus on the seismic response. The model comprises description of the monolithic structures, while prefabricated frame structures are ignored and replaced by external masses. Sensitivity study of the selected dynamic characteristics of the model with respect to data uncertainties is considered. Uncertainty of the model is considered in terms of masses of removed structures and wall stiffness. Seismic input is represented by the site specific free‐field ground response acceleration spectra. The sensitivity study concerns variations of frequencies and acceleration of in‐structure horizontal response spectra at specified points. Maximal bending moments are also considered. It was obtained that the reactor level is not sensitive to the uncertainties considered, while discernable sensitivity was detected at the top level of the structure. Santrauka Pateikta Ignalinos atominės elektrinės pastato erdvinio baigtinių elementų dinaminio modelio kūrimo koncepcija, išnagrinėtas šio modelio jautrumas keičiamoms masėms ir sienų standumui. Parodyta, kaip šie keičiami dydžiai turi įtaką dažniams, horizontaliems tam tikrų nagrinėjamų taškų atsako spektrams, lenkimo momentų persiskirstymui ir jų didžiui. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: Ignalinos AE, baigtinių elementų modelis, savųjų dažnių ir seisminė analizė, plyno lauko spektras, atsako spektras

On Efficiency of Parallel Solvers for the Blood Flow through Aortic Valve

Mathematical modelling of cardiac haemodynamics presents a great challenge to the computational scientists due to numerous numerical issues and required computational resources. In this paper, we study the parallel performance of 3D simulation software for the blood flow through the aortic valve. The fluid flow problem with the open aortic valve leaflets is formulated and solved in parallel. The choice between the segregated and coupled numerical schemes is discussed and investigated. We present and compare the parallel performance results of both types of parallel solvers. We investigate their strong and weak scalability

Investigation of fracture of inhomogeneous cast iron specimens

The proposed J-integral calculation technique in the piece-wise linear fatigue crack front has been used investigating SIF in the inhomogeneous cast iron specimens with defect and graphite voids. The influence of crack length and front, size and position of voids on SIF have been investigated and the increase of SIF by 15% has been obtained. Stress-strain state analysis of inhomogeneous cast iron specimens was carried out using FE code ANSYS

Generation of the unstructured fe-grids for complex 2d objects/Nestruktūrinių be tinklų generavimas sudėtingiems dvimačiams objektams

For the numerical simulation of engineering problems, the finite element method (FEM) is among the most popular approaches. One of the main concerns in a finite element analysis is the adequacy of the finite element grid. The accuracy of the FEM depends on the size, shape and placement of the elements. On the other hand, the total computational cost is determined by the total number of elements in FE model. An increased accuracy can be obtained by the global reduction of the element size, but this can be characterised by drastically increased computational cost. Thus, in many engineering applications it is desirable to generate not regular FE mesh with finer grid in the regions where accuracy of numerical simulation is of most importance and with more coarse grid in the other regions. In this paper we present a new approach to the grid generation of the multimaterial or multidomain engineering systems by the advancing front technique. This technique has proved successful in generating unstructured meshes in two and three dimensions [1–9]. The algorithm of the technique is summarised in section 2. Common for all approaches of advancing front mesh generation is that the generation problem is divided into three parts. First, the specification of the mesh size attributes, second, the discretisation of the boundaries, and, third, the discretisation of the interior of the domain. In the advancing front technique the front is defined as the boundary between the gridded and ungridded region. The key algorithmic step that must be addressed to advancing front methods is the proper introduction of new elements into the ungridded region. For triangular and tetrahedral grids the elements are introduced sequentially one at a time. The most obvious advantage of the advancing front method is that it directly incorporates free form geometry. Direct implementation of the advancing front technique for multimaterial or multidomain engineering applications is still challenging. Grid generation in the place of few materials or domain contact must ensure the compatibility of nodes on common boundary segments (nodes on common boundary segments must be in the same positions). The advancing front technique does not include non-convex domain, so at the first step non-convex domain of discretisation is decomposed into few convex subdomains. The subdomain of interest must be defined by describing a course background mesh of triangle elements, covering the entire multidomain region, which forms the input for finite element analysis. In this work, a black box architecture expert system has been developed which incorporates the information about the object geometry as well as the boundary and loading conditions, distribution of materials characteristics to generate an a priori (before the finite element analysis is carried out) mesh which is more refined around the critical regions (singularities, re-entrant corners, regions with high-stress concentration, etc) of the problem domain. This system uses a new concept of subtracting to locate the critical regions in the domain and to assign priority and mesh size to them. This involves the decomposition of the original structure into substructures (or primitives) for which an initial and approximate analysis can be performed by using analytical solutions and heuristics. When incorporated into and compared with the traditional approach to the adaptive finite element analysis, it is expected that the proposed approach, which starts the process with near optimal meshes, will be more accurate and efficient. Several numerical examples are presented and discussed. Examples demonstrate that our approach enables to generate the compatible meshes for multimaterial or multidomain problems. The quality of meshes is good, there are no ill-shaped elements. By the proposed expert system we can generate the mesh for any complex structure. The generation of 2D meshes is only the first step using the proposed expert system; in future we shall extend it for 3D meshes. During the last decade a lot of research has been devoted to extension of the advancing front technique to the parallel computers [8, 10, 11]. But the application of the technique to parallel processors is still challenging. In fact, we have to solve how to minimise inter-processor communication during mesh generation of subdomains. The proposed expert system for complex structures grid generation enables to use it with parallel computers. At the first step the domain of discretisation is decomposed into subdomains and all the surfaces defining the boundaries of subdomains to be gridded are triangulated. Later all subdomains can be meshed concurrently and no more inter-processor communication is required. The master task sends to workers tasks information about dividing common boundaries and information of each subdomain. The workers tasks receive their subdomain data and mesh their subdomain. Later the master receives the information from the workers tasks and joins gridded subdomains to one structure, ensuring the compatibility of nodes on common boundaries. So this suggested expert system enables to minimise the communications and costs of computations. The implementation of the expert system to parallel processors is to be done in the future. First Published Online: 26 Jul 201

Application of adaptive finite elements for solving elastic-plastic problem of SENB specimen

The proposed adaptive finite element analysis technique without transfer of variables is used for solving elastic-plastic problem of SENB specimen. The material nonlinear problem has been solved in iterative manner from the beginning till the fixed value of loading where new adaptive FE mesh was generated. Comparison of stresses, obtained solving material and geometrical nonlinear problems with the finest FE models, has been done with solutions presented in the literature. The modelling was carried out using FE code ANSYS

Mechanical properties and cyclic fracture behavior of differently heat-treated steel

Static mechanical, dynamic and resistance to cyclic loading properties obtained for differently heat-treated low carbon steel AISI 4130. Insignificant change of chemical content and heat-treatment change hardness, strength, ductility properties, impact resistance and threshold value of fatigue crack propagation. An analysis of CT specimens’ fractured views performed using SEM shows relationship of material microstructure with cyclic fracture

Static and cyclic strength of structural carbon and modified steels

In the article there are presented the results of experimental analytical study of the similar chemical composition but differently heat-treated structural steel: mechanical properties and resistance to cyclic loading. The indicators of strength, plasticity and cyclic failure process were determined. Fracture analysis of compact specimens (CT) was performed with SEM. It was attempted to validate the relation of mechanical properties (Rm = 500 MPa for CS500 steel and Rm = 700 MPa for CS700 steel) with stress intensity factor (ΔKth = 18 MPa∙√m for CS500 steel and ΔKth = 10 MPa∙√m for CS700 steel)

Investigation of contact behaviour of elastic layered spheres by FEM

Normal contact behaviour of two elastic-plastic layered spheres was investigated by the Finite Element Method (FEM) and role of specified distinct particle's parameters was examined. The particle consists of a relatively stiff elastic skin-layer and relatively soft core substrate. Modelling is made in the frame of the Hertz theory applied to homogeneous spheres. Contact force-displacement relationship as the main target of applications in DEM is basically studied by the FEM analysis. Contact behaviour is defined by the dimensionless effective elasticity modulus expressed finally in terms of elasticity modulus of core substrate and thickness of the layer

Fatigue strength investigation of four type cast irons specimens

In this paper data about four types cast irons chemical composition, microstructure, static mechanical properties, durability and cyclic fracture toughness is given. Ultimate stress obtained using cylindrical specimens of diameters 8-14 mm with circular notch are σu = 403-692 MPa. Endurance limit values of notched specimens are σ0 = 85-96 MPa. The performed analysis of breaks shows that heterogeneities and defects (voids) formation have an influence on static and cyclic fracture, because they change the crack front and shape of final fracture’s zone. The values of cyclic fracture toughness obtained according to the shape of final fracture’s zone are Kc = 10-26 MPa m . The obtained data allows deciding about the suitability of cast irons for structural elements production