1. Numerical solving of dynamic thermography inverse problem for skin cancer diagnosis based on non-Fourier bioheat modelIvan Dominik Horvat, Jurij Iljaž, 2025, original scientific article Abstract: This paper presents numerical solving of the inverse bioheat problem to estimate four skin cancer parameters; diameter, thickness, blood perfusion rate and thermal relaxation time, based on the thermal response on the skin surface obtained by dynamic thermography and numerical skin cancer model, which can greatly enhance dynamic thermography diagnostics. To describe the heat transfer inside biological tissue and thermal behavior during the dynamic thermography process as realistic as possible, the non-Fourier dual-phase-lag bioheat model was used, as well as skin cancer model has been composed of multilayered healthy skin, embedded skin tumor and subcutaneous fat and muscle. Boundary element method has been used to solve a complex non-Fourier bioheat model to simulate dynamic thermography based on the skin cancer model and guessed searched parameters to obtain the thermal response on the skin surface during the cooling and rewarming phase using a cold air jet provocation, which is needed for the solution of the inverse bioheat problem. The inverse problem has been solved by optimization approach using the hybrid Levenberg-Marquardt optimization method, while the measurement data has been generated numerically with known exact tumor parameters and added noise, to evaluate the accuracy and sensitivity of the solution. Inverse problem solution has been tested for two different thermal responses; absolute temperature and temperature difference response, as well as for two different tumor stages; early stage or Clark II and later stage or Clark IV tumor. All important tumor parameters were successfully retrieved, especially the diameter and relaxation time, even for the high level of noise, while the accuracy of obtained parameters is slightly better using absolute temperature response. The results demonstrate the robustness of the method and a promising way for early diagnosis. The findings contribute to improving bioheat modeling in biological tissues, solving inverse bioheat problems and advancing dynamic thermography as a non-invasive tool for early skin cancer diagnosis.
Keywords: numerical modeling, dynamic thermography, inverse problem, non-Fourier bioheat transfer, dual-phase-lag model, boundary element method, Levenberg-Marquardt optimization
Published in DKUM: 09.12.2025; Views: 0; Downloads: 6
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2. A novel data-driven surrogate approach for fast evaluation of the dynamics of soft ellipsoidal micro-particles in dilute viscous flowJana Wedel, Ivan Dominik Horvat, Nejc Vovk, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2026, original scientific article Abstract: We present a novel data-driven surrogate approach for fast evaluation of the deformation dynamics of soft particles, both initially spherical and ellipsoidal, suspended in external flows, specifically predicting the hydrodynamic tractions on the particle surface. The core of the approach relies on expressing the required force dyad as a linear combination of velocity gradient components, modulated by form coefficients. These coefficients scale shear, rotational, and extensional flow contributions to the velocity gradient. Two training strategies are proposed: one utilizing analytical data, which enables a computational speedup, and another based on data obtained with 3D direct numerical simulations (DNS) using the boundary element method (BEM), with the latter demonstrating the feasibility of this approach even in the absence of analytical solutions. Validation against established literature benchmarks confirms the model’s accuracy in three scenarios: (i) ellipsoidal particles in the quasi-rigid limit in pipe flow, (ii) initially spherical particles in shear flow, and (iii) initially ellipsoidal particles in shear flow. In all cases, the data-driven surrogate approach achieves excellent agreement with reference results. This work establishes a foundation for extending our data-driven approach to flow-induced deformations of soft particles of more complex particle shapes, such as superellipsoids and other non-ellipsoidal geometries, where no analytical traction expression is available.
Keywords: neural network, pseudo-rigid bodies, Barycenter and shape dynamics, Lagrangian particle tracking
Published in DKUM: 27.11.2025; Views: 0; Downloads: 2
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3. Numerical modeling of non-Fourier bioheat transfer in multilayer biological tissue using BEM to simulate dynamic thermography in skin tumor diagnosticsIvan Dominik Horvat, Jurij Iljaž, 2025, original scientific article Abstract: This paper presents a novel approach for modeling non-Fourier dual-phase-lag bioheat transfer in multilayer biological tissue, aimed at simulating dynamic thermography for the early detection of skin tumors at Clark II and IV stages. The proposed algorithm, based on the boundary element method, enables the assignment of distinct thermophysical properties and non-Fourier relaxation time parameters to each tissue layer, thereby enhancing the realism of bioheat transfer modeling. Results show that accounting for non-Fourier effects significantly impacts the transient thermal contrast between tumor and healthy skin, particularly in Clark IV tumors and at higher relaxation times. These findings support the development of more accurate and physiologically realistic models of heat transfer in complex biological structures, and advance the application of dynamic thermography in early skin tumor detection and the diagnosis of other dermatological conditions.
Keywords: numerical modeling, non-Fourier heat transfer, bioheat transfer, dual-phase-lag model, boundary element method, dynamic thermography
Published in DKUM: 03.11.2025; Views: 0; Downloads: 6
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4. Quadratic time elements for time-dependent fundamental solution in the BEM for heat transfer modelingIvan Dominik Horvat, Jurij Iljaž, 2024, original scientific article Abstract: In this paper, a quadratic time interpolation for temperature and a linear time interpolation for fluxes are implemented for the parabolic (time-dependent) fundamental solution-based scheme for solving transient heat transfer problems with sources using the subdomain BEM (boundary element method), which is the main innovation of this paper. The approach described in this work to incorporate the quadratic time variation does not require doubling the number of equations, which is otherwise required in the BEM literature, for the discretized problem to be well-conditioned. Moreover, the numerical accuracy, compared over an unprecedented range of the Fourier number (Fo) and source strength values, can help in selecting the appropriate scheme for a given application, depending on the rate of the heat transfer process and the included source term. The newly implemented scheme based on the parabolic fundamental solution is compared with the well-established elliptic (Laplace) scheme, where the time derivative of the temperature is approximated with the second-order finite difference scheme, on two examples.
Keywords: quadratic time elements, time-dependent fundamental solution, heat transfer modeling, boundary element method
Published in DKUM: 07.05.2025; Views: 0; Downloads: 10
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5. Določitev kritične velikosti razpoke v kombinirano obremenjeni gredi : magistrsko deloIvan Dominik Horvat, 2021, master's thesis Abstract: Pogonske gredi železniških vozil predstavljajo kritični element, ki je najbolj obremenjen med zagonom vozila. V praksi se je izkazalo, da se na pogonskih gredeh v osrednjem delu na mestu razširitve gredi za nased pesta zobnika lahko pojavijo prečne utrujenostne razpoke, ki v skrajnem primeru lahko zlome pogonsko gred. Namen magistrske naloge je raziskati napetostne pogoje, ki nastopijo med zagonom vozila in višino faktorja intenzitete napetosti, ki je lahko posledica risa med struženjem gredi ali lokalnih plitvih površinskih razpok. Napetostni pogoji so določeni z upoštevanjem sil na zobniku ter dimenzijskih razmer v kritičnem delu gredi in lastnosti materiala gredi. S pomočjo eksperimentalno opravljenih preizkušanj materiala gredi so določene natezne lastnosti ter na osnovi lomnomehanskih statičnih testov odpornostne krivulje materiala in dinamičnih testov so določeni parametri hitrosti rasti razpoke, kot tudi občutljivost materiala na iniciacijo utrujenostne rasti razpoke. Rezultati numeričnih simulacij kažejo, da faktor intenzitete napetosti pri razpoki globine 0,2 mm, ki je povprečna globina risa po struženju materiala je v rangu faktorja intenzitete za iniciacijo utrujenostne rasti razpoke. Inicirana utrujenostna razpoka, se lahko na to utrujenostno širi z vsakim zagonom, do svoje kritične velikosti. Obenem je ugotovljeno, da rast utrujenostne razpoke je dovolj počasna, da je možno med rednimi 6 mesečnimi pregledi na kritičnih mesti pravočasno zaznati prisotnost razpoke preden doseže svojo kritično velikost ter s tem gred z razpoko pravočasno odstraniti z železniškega vozila.
Keywords: mehanika loma, eksperimentalna mehanika loma, normalizacijska metoda, SINTAP, ASTM E1820-1, železniška pogonska gred, razpoka, utrujanje, faktor intenzitete napetosti, numerična simulacija po metodi končnih elementov, napetostna analiza
Published in DKUM: 09.03.2021; Views: 1227; Downloads: 182
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