Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 55) Show all publications
Reddy, G. M., Vynnycky, M. & Cuminato, J. A. (2019). An efficient adaptive boundary algorithm to reconstruct Neumann boundary data in the MFS for the inverse Stefan problem. Journal of Computational and Applied Mathematics, 349, 21-40
Open this publication in new window or tab >>An efficient adaptive boundary algorithm to reconstruct Neumann boundary data in the MFS for the inverse Stefan problem
2019 (English)In: Journal of Computational and Applied Mathematics, ISSN 0377-0427, E-ISSN 1879-1778, Vol. 349, p. 21-40Article in journal (Refereed) Published
Abstract [en]

In this exposition, a simple practical adaptive algorithm is developed for efficient and accurate reconstruction of Neumann boundary data in the inverse Stefan problem, which is a highly nontrivial task. Primarily, this algorithm detects the satisfactory location of the source points from the boundary in reconstructing the boundary data in the inverse Stefan problem efficiently. To deal with the ill-conditioning of the matrix generated by the MFS, we use Tikhonov regularization and the algorithm is designed in such a way that the optimal regularization parameter is detected automatically without any use of traditional methods like the discrepancy principle, the L-curve criterion or the generalized cross-validation (GCV) technique. Furthermore, this algorithm can be thought of as an alternative to the concept of Beck's future temperatures for obtaining stable and accurate fluxes, but without it being necessary to specify data on any future time interval. A MATLAB code for the algorithm is discussed in more-than-usual detail. We have studied the effects of accuracy and measurement error (random noise) on both optimal location and number of source points. The effectiveness of the proposed algorithm is shown through several test problems, and numerical experiments indicate promising results.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Inverse Stefan problem, Method of fundamental solutions, Tikhonov regularization, Neumann data, Adaptive algorithm
National Category
Other Mathematics
Identifiers
urn:nbn:se:kth:diva-241297 (URN)10.1016/j.cam.2018.09.004 (DOI)000454969100002 ()2-s2.0-85054454052 (Scopus ID)
Note

QC 20190222

Available from: 2019-02-22 Created: 2019-02-22 Last updated: 2019-02-22Bibliographically approved
McKee, S., Vynnycky, M. & Cuminato, J. A. (2019). An elementary diffusion problem, Laplace transforms and novel mathematical identities. Journal of Computational and Applied Mathematics, 353, 113-119
Open this publication in new window or tab >>An elementary diffusion problem, Laplace transforms and novel mathematical identities
2019 (English)In: Journal of Computational and Applied Mathematics, ISSN 0377-0427, E-ISSN 1879-1778, Vol. 353, p. 113-119Article in journal (Refereed) Published
Abstract [en]

While studying a problem in biomedical research a simple diffusion problem arose which admitted a solution by Fourier transforms. It was natural to ask if the same problem could be solved by Laplace transforms. In this note, we provide three solution techniques using Laplace transforms, with the last leading to a number of novel mathematical identities.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Fourier transforms, Laplace transforms
National Category
Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-246417 (URN)10.1016/j.cam.2018.12.016 (DOI)000463303300007 ()2-s2.0-85059808575 (Scopus ID)
Note

QC 20190329

Available from: 2019-03-29 Created: 2019-03-29 Last updated: 2019-04-29Bibliographically approved
Vynnycky, M., Mckee, S., Meere, M., McCormick, C. & McGinty, S. (2019). Asymptotic analysis of drug dissolution in two layers having widely differing diffusivities. IMA Journal of Applied Mathematics, 84(3), 533-554
Open this publication in new window or tab >>Asymptotic analysis of drug dissolution in two layers having widely differing diffusivities
Show others...
2019 (English)In: IMA Journal of Applied Mathematics, ISSN 0272-4960, E-ISSN 1464-3634, Vol. 84, no 3, p. 533-554Article in journal (Refereed) Published
Abstract [en]

This paper is concerned with a diffusion-controlled moving boundary problem in drug dissolution, in which the moving front passes from one medium to another for which the diffusivity is many orders of magnitude smaller. The classical Neumann similarity solution holds while the front is passing through the first layer, but this breaks down in the second layer. Asymptotic methods are used to understand what is happening in the second layer. Although this necessitates numerical computation, one interesting outcome is that only one calculation is required, no matter what the diffusivity is for the second layer.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2019
Keywords
drug dissolution, moving boundary problem, asymptotics, two layers
National Category
Mathematics
Identifiers
urn:nbn:se:kth:diva-264160 (URN)10.1093/imamat/hxz002 (DOI)000493523200004 ()
Note

QC 20191210

Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2019-12-10Bibliographically approved
Kohlstädt, S., Vynnycky, M., Neubauer, A. & Gebauer-Teichmann, A. (2019). Comparative RANS turbulence modelling of lost salt core viability in high pressure die casting. Progress in Computational Fluid Dynamics, An International Journal, 19(5), 316-327
Open this publication in new window or tab >>Comparative RANS turbulence modelling of lost salt core viability in high pressure die casting
2019 (English)In: Progress in Computational Fluid Dynamics, An International Journal, ISSN 1468-4349, E-ISSN 1741-5233, Vol. 19, no 5, p. 316-327Article in journal (Refereed) Published
Abstract [en]

In this work, the implementation of three turbulence models inside the open source C++ computational fluid dynamics (CFD) library OpenFOAM were tested in 2D and 3D to determine the viability of salt cores in high pressure die casting. A finite-volume and volume of fluid approach was used to model the two-phase flow of molten metal and air, with the latter being treated as compressible. Encouragingly, it is found that, although the choice of turbulence model seems to affect the dispersion of the two-phase interface, the force acting at the surface of the salt core depends only very weakly on the turbulence model used. The results were also compared against those obtained using the commercially available and widely-used casting software MAGMA(5).

Place, publisher, year, edition, pages
INDERSCIENCE ENTERPRISES LTD, 2019
Keywords
turbulence, RANS, volume-of-fluid method, OpenFOAM, high pressure die casting, HPDC, aluminium, lost cores, salt core viability
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-261057 (URN)10.1504/PCFD.2019.102054 (DOI)000484580300005 ()2-s2.0-85072018792 (Scopus ID)
Note

QC 20191001

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-01Bibliographically approved
Vynnycky, M. (2019). Continuous Casting. Metals, 9(6), Article ID 643.
Open this publication in new window or tab >>Continuous Casting
2019 (English)In: Metals, ISSN 2075-4701, Vol. 9, no 6, article id 643Article in journal, Editorial material (Refereed) Published
Place, publisher, year, edition, pages
MDPI, 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-255580 (URN)10.3390/met9060643 (DOI)000475356500027 ()2-s2.0-85068431004 (Scopus ID)
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-05Bibliographically approved
Vynnycky, M. & Lacaze, J. (2019). On the modelling of joint formation in dissolutive brazing processes. Journal of Engineering Mathematics, 116(1), 73-99
Open this publication in new window or tab >>On the modelling of joint formation in dissolutive brazing processes
2019 (English)In: Journal of Engineering Mathematics, ISSN 0022-0833, E-ISSN 1573-2703, Vol. 116, no 1, p. 73-99Article in journal (Refereed) Published
Abstract [en]

In this paper, earlier dissolutive wetting models describing the dynamics of an axisymmetric alloy drop spreading on pure metal substrate are extended to describe reactive wetting and subsequent joint formation in brazing processes. A two-dimensional time-dependent problem is formulated, and the model equations are nondimensionalized, revealing the possibilities for asymptotic model reduction. Whilst the numerical solution of the time-dependent problem, which contains two moving contact lines and would not in general be amenable to lubrication theory, is relegated to future work, the steady-state problem is analyzed in detail. The analysis offers an arguably more transparent alternative to an earlier energy minimization approach for finding the location of the meniscus, which ultimately constitutes the joint. The results of the present model are found to compare favourably to those of earlier experimental and theoretical work.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Asymptotic analysis, Dissolution, Wetting
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-255209 (URN)10.1007/s10665-019-10003-z (DOI)000471954000005 ()2-s2.0-85067245648 (Scopus ID)
Note

QC 20190903

Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-03Bibliographically approved
Vynnycky, M. & Assuncao, M. (2019). THE VANADIUM REDOX FLOW BATTERY: AN ASYMPTOTIC PERSPECTIVE. SIAM Journal on Applied Mathematics, 79(4), 1147-1172
Open this publication in new window or tab >>THE VANADIUM REDOX FLOW BATTERY: AN ASYMPTOTIC PERSPECTIVE
2019 (English)In: SIAM Journal on Applied Mathematics, ISSN 0036-1399, E-ISSN 1095-712X, Vol. 79, no 4, p. 1147-1172Article in journal (Refereed) Published
Abstract [en]

Asymptotic methods are used to analyze a time-dependent two-dimensional (2D) model for the operation of a vanadium redox flow battery-an energy storage technology that has attracted much attention recently. The model takes into account mass, momentum, and charge conservation involving a total of seven ionic species in two porous electrodes that are separated by a proton exchange membrane and attached to external recirculating tanks. In particular, we demonstrate a self-consistent asymptotic reduction of the original model. From this, we identify the presence of concentration boundary layers in each porous electrode at its interface with the membrane, and are able to explain the linear evolution in time of the inlet concentrations of the reacting ionic species-an assumption used in earlier models but never justified. The results of the asymptotic model, which ultimately requires only the numerical solution of four coupled nonlinear ordinary differential equations, are found to compare favorably with those of the original 2D transient problem, which involves 11 coupled nonlinear partial differential equations and two algebraic relations. The solution of the fully reduced asymptotic model is found to require around 300 times less computational time than that of the original model.

Place, publisher, year, edition, pages
SIAM PUBLICATIONS, 2019
Keywords
asymptotics, vanadium redox flow battery, electrochemistry
National Category
Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-260220 (URN)10.1137/18M1168984 (DOI)000483938900001 ()2-s2.0-85071942089 (Scopus ID)
Note

QC 20190927

Available from: 2019-09-27 Created: 2019-09-27 Last updated: 2019-09-27Bibliographically approved
Vynnycky, M., Saleem, S. & Fredriksson, H. (2018). An asymptotic approach to solidification shrinkage-induced macrosegregation in the continuous casting of binary alloys. Applied Mathematical Modelling, 54, 605-626
Open this publication in new window or tab >>An asymptotic approach to solidification shrinkage-induced macrosegregation in the continuous casting of binary alloys
2018 (English)In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 54, p. 605-626Article in journal (Refereed) Published
Abstract [en]

The modelling of macrosegregation in the continuous casting of alloys normally requires resource-intensive computational fluid dynamics (CFD). By contrast, here we develop an asymptotic framework for the case when macrosegregation is driven by solidification shrinkage; as a first step, a binary alloy is considered. Systematic asymptotic analysis of the steady-state two-dimensional mass, momentum, heat and solute conservation equations in terms of the shrinkage parameter indicates that the overall problem can be reduced to a hierarchy of decoupled problems: a leading-order problem that is non-linear, and a sequence of linear problems, with the actual macrosegregation of the solute then being determined by means of one-dimensional quadrature. A numerical method that solves this sequence is then developed and implemented, and yields realistic macrosegregation profiles at low computational cost.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE INC, 2018
Keywords
Continuous casting, Binary alloys, Macrosegregation
National Category
Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-222171 (URN)10.1016/j.apm.2017.10.012 (DOI)000423005000037 ()2-s2.0-85038207280 (Scopus ID)
Note

QC 20180207

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2018-02-07Bibliographically approved
Vynnycky, M. (2018). Applied mathematical modelling of continuous casting processes: A review. Metals, 8(11), Article ID 928.
Open this publication in new window or tab >>Applied mathematical modelling of continuous casting processes: A review
2018 (English)In: Metals, ISSN 2075-4701, Vol. 8, no 11, article id 928Article in journal (Refereed) Published
Abstract [en]

With readily available and ever-increasing computational resources, the modelling of continuous casting processes—mainly for steel, but also for copper and aluminium alloys—has predominantly focused on large-scale numerical simulation. Whilst there is certainly a need for this type of modelling, this paper highlights an alternative approach more grounded in applied mathematics, which lies between overly simplified analytical models and multi-dimensional simulations. In this approach, the governing equations are nondimensionalized and systematically simplified to obtain a formulation which is numerically much cheaper to compute, yet does not sacrifice any of the physics that was present in the original problem; in addition, the results should agree also quantitatively with those of the original model. This approach is well-suited to the modelling of continuous casting processes, which often involve the interaction of complex multiphysics. Recent examples involving mould taper, oscillation-mark formation, solidification shrinkage-induced macrosegregation and electromagnetic stirring are considered, as are the possibilities for the modelling of exudation, columnar-to-equiaxed transition, V-segregation, centreline porosity and mechanical soft reduction.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
Asymptotic analysis, Continuous casting, Numerical simulation
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-246539 (URN)10.3390/met8110928 (DOI)000451735100067 ()2-s2.0-85057280519 (Scopus ID)
Note

QC 20190319

Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-03-19Bibliographically approved
Lacaze, J., Jacques, B., Mazet, T. & Vynnycky, M. (2018). Numerical Simulation of Brazing Aluminium Alloys with Al-Si Alloys. Transactions of the Indian Institute of Metals, 71(11), 2623-2629
Open this publication in new window or tab >>Numerical Simulation of Brazing Aluminium Alloys with Al-Si Alloys
2018 (English)In: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 71, no 11, p. 2623-2629Article in journal (Refereed) Published
Abstract [en]

Joining parts using low-melting temperature alloys has long been used for manufacturing complex components such as heat exchangers made of aluminium alloys. Investigations of the process have shown that core/clad interaction during heating and brazing can lead to a significant decrease in the amount of liquid available for joint formation. This study presents a transient one-dimensional model for the process that takes into account the diffusion of silicon and the movement of the core/clad interface, with the model equations being implemented in the finite element software COMSOL Multiphysics;the results are compared to literature experimental data. Silicon profiles in the core are well described, while there appears a significant difference between predicted and experimental values of remaining clads which suggest a strong effect of silicon diffusion and liquid penetration at core grain boundaries.

Place, publisher, year, edition, pages
SPRINGER INDIA, 2018
Keywords
Brazing, Aluminium alloys, Solid-state diffusion, Melting
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-240017 (URN)10.1007/s12666-018-1415-8 (DOI)000449788900003 ()2-s2.0-85053861789 (Scopus ID)
Note

QC 20181210

Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2018-12-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8318-1251

Search in DiVA

Show all publications