Vahid Tamimi

Accurate estimation of modal damping ratios is essential for predicting and controlling the dynamic response of multi-degree-of-freedom (MDOF) structures, particularly in bridge and structural vibration studies. Despite the availability of various methods for estimating damping ratios in MDOF systems, most approaches rely on modal decoupling, which often involves considerable complexity and effort. This work introduces two approaches that eliminate the need for modal decoupling: a filter-based method and an improved Half-Quadratic Gain Method (HQGM). The filter-based approach extracts decay characteristics directly from displacement signals using frequency-domain filtering and logarithmic envelope analysis, achieving damping ratio estimates within 3% error for both free and forced vibrations and for systems with low or high damping. The HQGM, originally formulated for single-degree-of-freedom systems, is extended here to MDOF systems and further enhanced by a correction formula that suppresses coupling-induced secondary peaks in frequency response functions. Comparative analysis demonstrates that while the original HQGM performs well in weakly coupled systems, the improved HQGM yields superior accuracy under strong coupling conditions. Both methods provide a robust framework for identifying damping characteristics across a wide range of dynamic systems. The proposed techniques offer practical advantages for structural engineering applications, where damping properties are difficult to measure directly.

This review paper presents the recent advances in the numerical modelling of wave–structure–seabed interactions. The processes that are involved in wave–structure interactions, which leads to sediment transport and scour effects, are summarized. Subsequently, the three most common approaches for modelling sediment transport that is induced by wave–structure interactions are described. The applicability of each numerical approach is also included with a summary of the most recent studies. These approaches are based on the Reynolds-Averaged Navier–Stokes (RANS) equations for the fluid phase, and mostly differ in how they tackle the seabed response. Finally, future prospects of research are discussed.

The relative incompetency of rectangular galloping excavators against conventional circular VIV harvesters is already known. In this experimental study, the hydroelastic energy performances of new right-angle isosceles triangular cylinder against circular, square and diamond cross-sections are investigated. The triangular cylinder displays VIV or galloping type of response in four different symmetrical and unsymmetrical configurations tested. The results show the distinct higher overall galloping energy performance of the triangular cylinder in Config. 2 among other VIV and galloping harvesters. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) is employed to order the remaining tested cross-sections using the averaged and maximum values of the mechanical power and efficiency as criteria. The TOPSIS algorithm shows that the VIV diamond and circular harvesters stay at the second and third places of the energy performance, respectively. The preference value of the diamond and circular cross-sections are almost comparable but are less than half of that in Config. 2. In general, the sharp-edge cylinders display superior energy performance over circular cross-section. However, the axisymmetric circular cylinders, because of their omnidirectional performances, are more efficient in places with the varying flow direction.