sustainability Article Modernization of the Infrastructure of Marine Passenger Port Based on Synthesis of the Structure and Forecasting Development Sre´ cko Krile 1 , Nikolai Maiorov 2, * and Vladimir Fetisov 2   Citation: Krile, S.; Maiorov, N.; Fetisov, V. Modernization of the Infrastructure of Marine Passenger Port Based on Synthesis of the Structure and Forecasting Development. Sustainability 2021, 13, 3869. https://doi.org/10.3390/ su13073869 Academic Editor: Grant Bigg Received: 25 February 2021 Accepted: 26 March 2021 Published: 31 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Electrical Engineering and Computing Department, University of Dubrovnik, 20000 Dubrovnik, Croatia; srecko.krile@unidu.hr 2 Department of Systems Analysis and Logistics, Saint-Petersburg State University of Aerospace Instrumentation 2, 190000 Saint Petersburg, Russia; fet1vlad@yandex.ru * Correspondence: nmsoft@yandex.ru Abstract: Passenger seaports are new starting-points of urban development. They form a new independent industry, become new incentives for improving urban infrastructure and increase the tourist attractiveness of the city itself and the region. In view of changes in passenger service processes, changes in route ferry and cruise networks, due to COVID-19, the heads of ports and terminals set new strategic tasks to determine the directions for infrastructure modernization and forecast development. The regions of the Adriatic and Baltic Seas were chosen as the experimental base. To ﬁnd new answers, it is necessary to solve the problem of synthesizing the structure of a sea passenger port, taking into account all processes and services, the inﬂuence of the external environment, building a system of target functions and limiting conditions. Thus, the necessity of forming informed decisions on modernization based on the construction of new mathematical models is substantiated. A new function has been introduced that describes the inﬂuence of the external environment. Particular attention is given to the study of the mutual inﬂuence of the city and the sea passenger port in order to determine the need to improve transport accessibility and change the near-port transport space. The presented models of structure synthesis and target functions, models including functions of the inﬂuence of the external environment on the system “city infrastructure-sea passenger port-ferry company” allow at a qualitatively new level to solve the problem of forecasting development and form a system making decisions to improve the position of the passenger terminal in the sea region. The developed models and synthesis problem formation are applicable to sea passenger ports and terminals in other regions of the seas. The models are applicable both at the stage of creating a new marine terminal and during the study and subsequent modernization of the infrastructure. The presented new models allow the port manager to give answers to the questions of strategic development of sea passenger ports in sea regions. Keywords: structure synthesis; modeling; ferry network; cruise network; mathematical model; the Baltic Sea region; sea passenger port 1. Introduction Global changes in the world economy, changes in transport infrastructure, changes in society and widespread introduction of digital technologies directly affect the development and changes of ports, terminals and transport systems. Historically, there is a direct rela- tionship between the development of ports and the development of cities. However, today there is a signiﬁcant increase in the inﬂuence of such trends with competition in the market increasing environmental requirements and norms, the observed shortage of areas for ports and new terminals within urban boundaries, as well as new requirements for supply chain management and a number of others. Sustainability 2021, 13, 3869. https://doi.org/10.3390/su13073869 https://www.mdpi.com/journal/sustainability