en Offshore Structure مقاله پژوهشي Research Paper <span style="font-size:10.0pt"><span new="" roman="" style="font-family:" times="">In response to rising global energy demand and the urgent need to reduce greenhouse gas emissions, Offshore Wind Turbines (OWTs) have emerged as promising renewable energy solutions. Among deep-water support structures, semi-submersible platforms offer superior motion stability and design flexibility, but their high structural weight significantly affects construction and installation costs. This study compares five metaheuristic algorithms&mdash;Genetic Algorithm (GA), Ant Colony Optimization for Continuous Domains (ACO_R), Artificial Bee Colony (ABC), Firefly Algorithm (FA), and Particle Swarm Optimization (PSO)&mdash;for weight optimization of a four-column semi-submersible substructure supporting a Vertical Axis Wind Turbine (VAWT) with hexagonal pontoons. The algorithms were first validated with a reference platform optimized using the Generalized Reduced Gradient (GRG) method. They were then applied to minimize the VAWT substructure weight by optimizing pontoon and column geometry, spacing, and draft under hydrostatic stability, motion, airgap, and feasibility constraints. Each algorithm was executed five times, and Kolmogorov&ndash;Smirnov tests confirmed normality of optimized weight and Number of Function Evaluations (NFE). Analysis of Variance (ANOVA) indicated statistically significant differences among algorithms, and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) was used for multi-criteria decision-making, considering average weight, NFE, accuracy, variance, and stability. Results indicate that ACO_R achieved the highest rank, achieving ~37.6% (3690 tons) weight reduction. The findings demonstrate ACO_R&rsquo;s effectiveness as a decision-support tool for conceptual design of semi-submersible substructure of OWTs. However, it is expected that hydrodynamic loading, aero-structural coupling to be also considered for further detailed design.</span></span> Metaheuristic optimization,Semi-submersible VAWT,Statistical evaluation algorithm,Hexagonal pontoons,Multi-criteria decision 66 79 http://ijmt.ir/browse.php?a_code=A-10-31-1&slc_lang=en&sid=1 Zanyar Delgarm zanyardelgarm@gmail.com 10031947532846004491 10031947532846004491 No Sahand Univ. of Tech. Ahmad Reza Mostafa Gharebaghi mgharabaghi@sut.ac.ir 10031947532846004492 10031947532846004492 Yes Sahand University of Technology Arefeh Emami emami@hormozgan.ac.ir 10031947532846004493 10031947532846004493 No Univ. of Hormozgan