In this original final project, called “Modelling and control of semi-active fluid viscous dampers in structural vibration optimization” the behaviour and usefulness of a device referred to as “variable orifice fluid viscous damper” is analysed in the context of improving the dynamic response of structures. Nowadays, in the civil engineering field, the presence of strategies to act on the behaviour of structures subjected to external inputs such as earthquakes or wind gusts is more and more often present. These strategies in literature are divided into three main approaches: passive control, semi-active control, and active control. Passive control of structures consists in exploiting devices that are fixated on a certain behaviour that cannot be modified in real-time it can be also considered a redesign of the structure parameters.