Publications

2011

Aristovich K.Y., Khan S.H., Borovkov A.I. Investigation of optimal parameters for finite element solution of the forward problem in magnetic field tomography based on magnetoencephalography. Journal of Physics: Conference Series (Sensors & their Applications XVI), 2011, v.307, N1

     Abstract. This paper presents an investigation of optimal parameters for finite element (FE) solution of the forward problem in magnetic field tomography (MFT) brain imaging based on magnetoencephalography (MEG). It highlights detailed analyses of the main parameters involved and evaluates their optimal values for various cases of FE model solutions (e.g., steady-state, transient, etc.). In each case, a detail study of some of the main parameters and their effects on FE solution and its accuracy are carefully tested and evaluated. These parameters include: total number and size of 3D FE elements used, number and size of elements used in surface discretisation (of both white and grey matters of the brain), number and size of elements used for approximation of current sources, number of anisotropic properties used in steady-state and transient solutions, and the time steps used in transient analyses. The optimal values of these parameters in relation to solution accuracy and mesh convergence criteria have been found and presented.

2010 

Nemov A.S., Boso D.P., Voynov I.B., Borovkov A.I., Schrefler B.A. Generalized stiffness coefficients for ITER superconducting cables, direct FE modeling and initial configuration. Cryogenics, 2010, Volume 50, Issue 5, 304 - 314.
     Abstract. Superconducting coils are one of the key technical solutions used for generation of high magnetic field in modern tokamaks. Nb3Sn superconductivity depends not only on temperature and magnetic field as e.g. NbTi, but also on the strain state of the strands inside the conductor. It is hence very important to be able to predict the mechanical deformations due to manufacturing processes and operating conditions. The conductors for ITER, the International Thermonuclear Experimental Reactor currently under construction, have a complex structure that makes analytical estimations of stiffness applicable only for the first cabling stages. In this work, a wide range of numerical simulations has been performed, by using several types of finite element models. This paper shows some analytical estimations for stretching and twisting and compares them with the numerical results of the different models. Some comparisons with experimental tests are also presented. Furthermore, it is shown that direct finite element analyses are compulsory for higher cable stages, but need the knowledge of the initial configuration as precise as possible for meaningful simulations. This problem is also addressed in this paper.

 

Malinin L., Borovkov A., Voynov I., Pyak B., Pyak V. Modeling of Efficiency of Aerodynamic Devices on a Tractor-Trailer. Int. Journal of Aerodynamics. 2010, Vol. 1, No.2  pp. 206 - 219
Abstract: While trucking accounts for 60% of freight energy use in the US, aerodynamic drag is responsible for 65% of the total energy expenditure for a heavy truck at 70 miles per hour. Reducing the aerodynamic resistance of a heavy truck can significantly improve its fuel economy. While multiple aerodynamic devices have been proposed for heavy trucks, they do not always promote the most efficient operation, as they may hinder maneuvering and docking. This limited acceptance by the industry can be summarized as a contradiction: Aerodynamic devices are useful at cruising speed, but during docking or maneuvering they may be an obstacle to efficient operations. This contradiction can be resolved if the devices are only deployed or interact with the incoming flow at high speed. Examples are dynamic (foldable) side fairings and vortex generators (VGs). Computational Fluid Dynamics (CFD) modeling of the VGs under head and side wind conditions as shown that they are more efficient for side winds than for head winds.
Keywords: heavy trucks, aerodynamic resistance, foldable fairings, CFD modelling, vortex generators, computational fluid dynamics, aerodynamic efficiency, tractor-trailers, aerodynamics, heavy vehicles, manoeuvring, docking
 

2009

Novozhilov Yu.V., Mikhaluk D.S., Borovkov A.I., Gilyov E.E., Kemppinen M., Dufva K., Karttunen T., Koulu J. Simulation and Testing ot Stitched Glassfibre Laminates Fatigue Behaviour. Proc. 17th Int. Conf. on Composite Materials. 2009, Edinburgh, UK, paper A7:9, 9 p.  Abstract
     Summary. The goal of this paper is Finite Element (FE) stress analysis of stitched glassfibre composites. The stress distribution gives an idea of laminate fatigue behaviour and potential alarm zone locations. The research includes a FE simulation and an experimental study for laminates with different stitching parameters. Analysis is performed on meso-level: fiber bundles and matrix are considered, but not separate fibers. Bundle waviness, variable thickness and volume factor are taken into consideration.

Aristovich K., Antonova O., Khan S., Borovkov A. Fast-Processing Modelling Technology in ApplicaTion to the Complex Realistic Biomechanical Problems. Book of Abstracts of XXXVII Summer School "Advanced Problems in Mechanics" . 2009, St.Petersburg, Russia. p. 24.

Michailov A.A., Voinov I.B.  Borovkov A. I. Designing safe crackers. CAD CAM Report Nr.5, 2009, pp. 20-21. (www.cad-cam-report.de).
   Summary. This paper presents the methodology and some of the results of numerical solution of the 3-D structural analysis of a catalytic cracker, taking into account the effects of external fluids flow as well as overall mechanical and thermal stresses.Using the ANSYS CFX software it was simulated the air flow around the cracker. By varying the 22 parameters, it was performed a series of computations that focused on decreasing  the load on the nose pieces and defining the construction thicknesses with considering the Russian oil and gas standards.

Nemov A., Borovkov A., Schrefler B. Finite Element Modeling of the ITER Superconducting Cables Mechanical Behavior Using LS-DYNA Code. Proc. 7th  European LS-DYNA Conference. 2009, Salzburg, Austria, 9p.
   Summary. Superconducting cables are one of the key technical solutions used for generation of strong magnetic field in modern tokamaks. It is very important for engineers to be able to predict the mechanical deformations of superconducting cables because caused by them heat generation can brake required for normal operation temperature conditions. Superconducting cables for the ITER (International Thermonuclear Experimental Reactor) that is currently under construction have a complex structure that makes any analytical estimations hardly applicable for them. This paper reports on the solution of different mechanical problems for the ITER superconducting cable elements using LS-DYNA finite element code. Stretching, twisting and transverse pressing loadings are considered and results are compared with analytical estimations where possible.

Mikhaluk D., Voinov I., Borovkov A. Finite Element Modeling of the Arresting Gear and Simulation of the Aircraft Deck Landing Dynamics. Proc. 7th  European LS-DYNA Conference. 2009, Salzburg, Austria, 10p.
   Summary. Deck arresting gear is a special aerocarrier unit that is destined to provide efficient arrest of deck jetfighters with high deck landing speed (200-240 km/h). Arresting gear is a hydraulic plunger brake connected with takeup cable stretched across the deck, through the multiple block and tackle and spring damper elements. Jetfighters deck landing is one of the most complex and critical parts of the flight. It requires failurefree operation of the arresting gear system and skilled actions of the pilot. One of the factors that influences safety of the deck landing is the strength of the arresting gear structural elements and optimal “tuning” of the system for the arrest of the jetfighter with specific mass moving with specific velocity. In the current work a fullscale dynamic model of the deck arresting gear is created. It contains all basic elements of the real prototype and used to analyze the dynamic behavior of the arresting gear and tune it for specific conditions of the arrest. Main elements of the arresting gear are the cable and the hydraulic braking machine. The cable consists of two parts – takeup cable and braking cable. During deck landing the jetfighter grasps the takeup cable with a hook. The takeup cable is coupled with the braking cable that is designated to transfer jetfighter pull to the hydraulic braking machine. The latter is represented by hydrocylinder and accumulator where the kinetic energy of the fighter is transferred to the heat and then dissipated. The dynamic analysis was performed with use of LS-DYNA software. Standard capabilities of LS-DYNA do not enable performing adequate simulation of such complex nonlinear system, because due to feedback control system, some characteristics of the braking machine vary with change of other parameters. By that reason special software was developed that allows managing LS-DYNA and automatically run the process with multiple restarts. Developed dynamic model is used to obtain main parameters of the arresting process – change of the fighter displacement, velocity, acceleration vs. time, as well as pressure in the hydraulic elements of the braking machine.

Khan, S. H.   Aristovich, K. Y.   Borovkov, A. I.  Solution of the Forward Problem in Magnetic-Field Tomography (MFT) Based on Magnetoencephalography (MEG).  IEEE Transactions on Magnetics, 2009, Vol. 45,  Issue 3, 1416-1419
   Summary. This paper presents the methodology and some of the results of accurate solution of the forward problem in magnetic-field tomography based on magnetoencephalography for brain imaging. The solution is based on modeling and computation of magnetic-field distribution in and around the head produced by distributed 2-D cortical and 3-D volume lead current sources. The 3-D finite-element model of the brain incorporates realistic geometry based on accurate magnetic resonance imaging data and inhomogeneous conductivity properties. The model allows arbitrary placement of line, surface, and volume current sources. This gives flexibility in the source current approximation in terms of size, orientation, placement, and spatial distribution.

2008

Mikhaluk D., Voinov I., Borovkov A. Finite Element Modeling of the Arresting Gear and Simulation of the Aircraft Deck Landing Dynamics. Proc. 6th EUROMECH Nonlinear Dynamics Conf. (ENOC'2008). St.Petersburg, Russia. 2008. 5p.
   Abstract.
In the current work a full-scale dynamic model of the deck arresting gear is developed. Arresting gear is a special aero-carrier unit that is destined to provide efficient arrest of deck jet-fighters with high deck landing speed (200-240 km/h). It consists of a hydraulic plunger brake connected with take-up cable stretched across the deck, through the multiple block-and-tackle and spring-damper elements. The developed numerical model contains all basic elements of the real prototype and used to analyze the dynamic behavior of the arresting gear and tune it for specific conditions of the arrest.

Klyavin O., Michailov A., Borovkov A. Finite Element Modeling of the Crash-Tests for Energy Absorbing Lighting Column. Proc. 6th EUROMECH Nonlinear Dynamics Conf. (ENOC'2008). St.Petersburg, Russia. 2008. 5p.
   Abstract. Finite Element system LS-DYNA is used in this project to perform contact-impact non-linear dynamic analysis of the lighting column crash-test with vehicle. FE spatial discretization is achieved by the use of shell and solid elements. Developed 3D CAD and FEM models of different types of columns that allowed simulation of the following nonlinearities: impact at different vehicle speed, plasticity in column and vehicle parts, contact interaction between simulated objects, progressive damage in column laminates. The resultant simulated deceleration curves allowed calculation of head injury criteria (HIC) and safety estimation for all columns crash tests.

Mikhaluk D.S., TruongT.C., Borovkov A.I.,  Lomov S.V., Verpoest I. Experimental Observations and Finite Element Modelling of Damage Initiation and Evolution in Carbon/Epoxy Non-Crimp Fabric Composites.  Engineering Fracture Mechanics. Volume 75, Issue 9. 2008. 2751-2766. 
  
Abstract. Damage in carbon/epoxy non-crimp stitched fabric (NCF) reinforced composites, produced by the resin transfer moulding (RTM) process is described. Formation of the stitching loop results in a certain disturbance of the uniform placement of the fibres. These deviations in fibre placement produce resin-rich zones that can influence the mechanical behaviour of the composite part. Tensile tests on quadriaxial (45°/90°–45°/0°)s laminates are performed accompanied by acoustic emission (AE) registration and X-ray imaging. Early initiation of damage (matrix cracking) in plies with different fibre orientation has been detected. Damage sites correlate with the resin-rich zones 
created by the stitching. Finite element (FE) analysis is carried out to develop a model that describes damage of the NCF composites. Numerical multi-level FE homogenization is performed to obtain effective elastic orthotropic properties of NCF composite at micro (unit cell of unidirectional tow) and meso (fabric unit cell) levels. A hierarchical sequence of FE models of different scales is created to analyze in detail the 3D stress state of the NCF composite (meso unit cell). A multi-level submodeling approach is applied during FE analysis. Zones of matrix-dominated damage are predicted. A comparison of non-destructive testing results with computational model is performed. Fracture mechanics parameters of matrix crack are computed and cracks growth stability is studied.

Khan S.,  Aristovich Yu., Borovkov A. Matematical Modelling of Human Brain for Magnetic Field Tomography Based on Magnetoencephalography. Proc. 12th IMEKO TC1 & TC7 Joint Symposium on Man, Science & Measurement, 2008, Annecy, France, 191 - 194.

Aleman-Meza D., Borovkov A.I. Finite Modeling and Comparative Analysis of Effective Elastic Properties of Composites. 3. Granulated Composites. Applied Mechanics in the Americas. Vol.12. Proc. Tenth Pan American Congress of Applied Mechanics (PACAM X). Ed. Th. Attard. Cancun, Mexico. 2008. 37-40.

Aleman-Meza D., Borovkov A.I. Finite Modeling and Comparative Analysis of Effective Elastic Properties of Composites. 2. Fiber Reinforced Composites. Applied Mechanics in the Americas. Vol.12. Proc. Tenth Pan American Congress of Applied Mechanics (PACAM X). Ed. Th. Attard. Cancun, Mexico. 2008. 33-36.

Aleman-Meza D., Borovkov A.I. Finite Modeling and Comparative Analysis of Effective Elastic Properties of Composites. 1. Homogenization Methods. Applied Mechanics in the Americas. Vol.12. Proc. Tenth Pan American Congress of Applied Mechanics (PACAM X). Ed. Th. Attard. Cancun, Mexico. 2008. 353-356.