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From 14 to 16 July 2026, the 2nd Croatian–Chinese Workshop on Multiphysics – Advances in Multiphysics Modeling and Coupled Systems was held at the Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture at the University of Split. The workshop was co-chaired by Prof. Dragan Poljak (FESB, University of Split) and Prof. Zhuojia Fu (Hohai University, Nanjing, China). More information on the workshop can be found here.

In addition to researchers involved in the bilateral project, the workshop brought together participants from several University of Split faculties: Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, Faculty of Science and the Faculty of Maritime Studies. The workshop formed part of the activities of the Croatian–Chinese bilateral research project, jointly led by Prof. Dragan Poljak and Prof. Zhuojia Fu. Over the course of the three-day workshop, 20 researchers participated and 16 scientific presentations were delivered, fostering scientific exchange and strengthening collaboration between Croatian and Chinese research institutions in the field of multiphysics modeling and environmental applications.

Žarko Kovač gave a talk titled From Stochastic Models to Conservation Principles in Biophysical Oceanography, describing ongoing work on the PHOTOCLIM project. The Abstract if provided below: 

Since Harald Sverdrup's seminal 1953 formulation of the Critical Depth Hypothesis, the  interplay between turbulent mixing, light availability, and phytoplankton growth has remained   a central problem in biophysical oceanography. Sverdrup introduced the critical depth as the depth horizon at which vertically integrated primary production balances integrated losses,  providing the first mathematical explanation for the initiation of phytoplankton blooms. Despite its importance, several fundamental questions regarding the critical depth, compensation depth,  mixing, and bio-optical feedback have remained unresolved. This presentation revisits these classical concepts through a combination of analytical, stochastic, and dynamical systems approaches. Beginning with Sverdrup's original model, an exact analytical solution for the critical depth is derived using the Lambert W function. The model is then extended to include phytoplankton shading, revealing a biooptical feedback between biomass and light attenuation. Exact solutions for mixed-layer biomass and production at steady state are obtained, and a biooptical bifurcation emerges in which mixed-layer depth acts as the control parameter and the critical depth marks the bifurcation point. A complementary Lagrangian framework is developed to investigate the effects of turbulent mixing on individual phytoplankton cells. Using stochastic differential equations to describe vertical cell motion and applying Jensen's inequality and Itô's lemma, new expressions for average production and compensation depth are derived for intermediate mixing regimes. This probabilistic treatment demonstrates that mixing generally enhances primary production by deepening the effective compensation depth and provides a unified interpretation of compensation and critical depths across different mixing regimes. In the limit of weak mixing the compensation depth emerges naturally, whereas under strong mixing the critical depth becomes the relevant threshold.

Presentation can be downloaded below.