Arnas Kačeniauskas

Parallel discrete element simulation of poly-dispersed granular material

The paper presents parallel 3D DEM simulation of poly-dispersed material described by the normal size distribution. Static domain decomposition and message passing inter-processor communication have been implemented in the DEM code. A novel algorithm for moving particles that exchange processors has been incorporated in the domain decomposition framework. Parallel performance of the developed algorithm and software has been investigated by a series of benchmark tests conducting tri-axial compaction of material with different numbers of particles, heterogeneity ratios and compaction durations. The speed-up equal to 8.81 has been obtained on 10 processors of the distributed memory PC cluster. It has been shown that a drastic increase of computational expenses of simulation for the poly-dispersed material in terms of CPU time is associated with the increase of its heterogeneity. A contribution of the temporal evolution of microscopic behaviour has also been illustrated.

Structural Mechanics of Railguns in the Case of Discrete Supports

In this paper, numerical calculations concerning the dynamic behavior of a railgun are presented. At the first stage, the structural problem can be decoupled from electromagnetic phenomena as well as from the local projectile behavior. The magnetic pressure repelling the rails from each other and expanding with the speed of the projectile serves as a boundary condition for purely mechanical calculations. The particularity of the investigation is represented by the type of railgun housing. For some years, the ISL has been using laboratory housings of an open design allowing, for instance, to take flash radiographs during launch. The repelling forces are mainly taken by discrete supports in the form of steel bolts. These bolts are connected to bars made of glass fiber-reinforced plastics, while the rails are mounted on these bars. A 2-D finite-element model of a complex housing was developed in this paper. Bars, including rails, are described by plane-stress elements, while bolts, playing the role of discrete elastic supports, are presented by truss elements. The model is implemented using the ANSYS code. Deformation properties of the rail section and elastic supports are examined by considering a static solution, assuming constant loading. Differences between 2-D and conventional beam models being of importance for this kind of problem are briefly discussed. Transient analysis was performed for a set of constant loading velocities (600-1600 m/s) and for the experimentally derived transient-loading profile. The latter was obtained in the railgun experiments performed using the ISL-railgun EMA3 with a caliber of 15times30 mm2 and typical muzzle velocities up to 1600 m/s as well as peak currents of about 600 kA.

Manganite Sensor for Measurements of Magnetic Field Disturbances of Pulsed Actuators

Magnetic field sensors based on polycrystalline La0.83Sr0.17MnO3 films were used to measure the magnetic field distribution and disturbances during the operation of an electromagnetic launcher. Hollow cylinders made from dural aluminum and iron were used as propelled objects inside the solenoidal coil. The obtained results revealed the ability of manganite sensors to rapidly measure changing high magnetic fields of arbitrary waveforms.

The comparison of two domain repartitioning methods used for parallel discrete element computations of the hopper discharge

Two methods are employed for dynamic domain decomposition of hopper discharge.Implementation of the k-way graph partitioning method in DEM codes is more complex.A higher speed-up is measured, applying the recursive coordinate bisection method.Parallel efficiency of 0.87 is attained simulating 5.1i?106 particles on 2048 cores. The paper presents an application of two domain repartitioning methods to solving hopper discharge problem simulated by the discrete element method. Quantitative comparison of parallel speed-up obtained by using the multilevel k-way graph partitioning method and the recursive coordinate bisection method is presented. The detailed investigation of load balance, interprocessor communication and repartitioning is performed. Speed-up of the parallel computations based on the dynamic domain decomposition is investigated by a series of benchmark tests simulating the granular visco-elastic frictional media in hoppers containing 0.3i?106 and 5.1i?106 spherical particles. A soft-particle approach is adopted, when the simulation is performed by small time increments and the contact forces between the particles are calculated using the contact law. The parallel efficiency of 0.87 was achieved on 2048 cores, modelling the hopper filled with 5.1i?106 particles.

Computation and visualization of discrete particle systems on gLite-based grid

Three-dimensional simulation of discrete particle systems is performed by the discrete element method (DEM) software on the gLite-based BalticGrid infrastructure. The performance of a parallel algorithm for particles exchanging processors is investigated by using a number of benchmarks. Polydispersed particle systems are visualized by a novel grid e-service VizLitG designed for convenient access and interactive visualization of remote data files located on the grid. Partial dataset transfer from the storage element is implemented in the visualization e-service. The efficiency tests of VizLitG are performed on the datasets of different sizes. Two granular problems associated with triaxial compaction and hopper discharge are solved.

Development of cloud services for patient-specific simulations of blood flows through aortic valves

The paper presents the development of cloud software services for patient-specific computational analysis of blood flows through the aortic valve on a private university cloud. The main focus is on the software service level at the top of the provided computational platform. Blood flow through the aortic valve was considered as a pilot application of the OpenStack cloud infrastructure. A modelling software environment based on ANSYS Fluent was developed as a software service (SaaS) for the numerical analysis of low flow, low pressure gradient aortic stenosis. Segmentation software services were designed to deal with the patient-specific issues of the computational analysis. User-friendly management tools were developed using Apache jclouds API to enhance the management of OpenStack cloud infrastructure and to increase the accessibility of the required software. The performance of the cloud infrastructure was assessed by testing CPU, memory bandwidth, disk I/O and the developed software service for medical computations. The performance measured on Xen hardware virtual machines, KVM virtual machines and Docker containers were compared with the performance obtained by using the native hardware.

VizLitG: Grid Visualization e-Service Enabling Partial Dataset Transfer from Storage Elements of gLite-based Grid Infrastructure

Grid visualization e-service VizlitG is developed for Lithuanian grid infrastructure based on gLite middleware. The client–server architecture of the e-service VizLitG is based on widely recognized web standards implemented in Java EE 6 platform and GlassFish application server. VizLitG is designed for convenient access and interactive visualization of remote data files located in storage elements of gLite-based grid infrastructure. Partial dataset transfer from the experimental storage element is developed in order to reduce the communication time and achieve interactive rates. The performance of VizLitG is evaluated visualizing poly-dispersed particle systems of different sizes in a geographically distributed grid. The attention is focused on the performance of data transfer from the storage elements and its contribution to the total benchmark time. Different types of software are employed for data transfer in order to present the quantitative comparison.

Controls-based approach for evaluation of information security standards implementation costs

AbstractAccording to the PricewaterhouseCoopers analysis, the average cost of a single information security and data protections breaches has increased twice during 2015 (Pricewaterhouse Coopers 2015). Amount of organizations who reported serious breach has also risen (from 9% in 2015 to 17% in 2016) (PricewaterhouseCoopers 2016). To achieve their goals criminals are using different techniques starting from Social engineering (phishing, whaling) and finishing with malware execution (such as ransomware) on target machines. Recent attacks (attack on Central Bank of Bangladesh, fraud attack on Mattel CEO and attack on Thailand state-run Government bank ATM) show, that criminals are very well organized, equipped and spend a lot of money and time to prepare their attacks. To protect themselves organizations are required to ensure security in depth principles and implement complex Security solutions, which are able to ensure the needed level of information security in appropriate costs.However, information secu...

Visualization of cracks by using the local Voronoi decompositions and distributed software

Local Voronoi decompositions are applied to extraction of crack surfaces.Cracks propagate in mono-dispersed particulate media simulated by the DEM.The geometry of crack surfaces is accurately defined by faces of the decomposition.Generation of local decompositions rather than global meshes reduces execution time.The sufficiently high speed-up of distributed visualization software is achieved. The paper presents a novel visualization technique for cracks propagating in mono-dispersed particulate material. The proposed technique is based on local space decompositions generated in fractured areas. The contact surfaces of the neighboring particles are defined by the local Voronoi decomposition generated according to the lattice topology employed in computations of the discrete element method. The visual model validation helps to indicate the regions of a highly deformed lattice, where the defects detected between the pairs of the neighboring particles on the lattice connections cannot be directly mapped onto the relevant edges of the Voronoi diagram. The parallel implementation of the visualization technique is based on the domain decomposition and two layers of ghost vertices and connections. The technique is implemented in the distributed visualization software VisPartDEM. Datasets of the elastic solid problem exhibiting non-uniform distribution of fracture force values are considered to validate the performance of the proposed technique. The parallel speed-up of the visualization software is investigated. The superior performance of the applied local technique is compared to the performance observed by using the standard global Voronoi algorithm.

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.