Introduction
This paper presents a theoretical investigation of the second-order steady horizontal and vertical drift forces acting on a vertical porous cylindrical body which is exposed to the action of regular plane waves propagating in finite depth waters. The examined body consists of a truncated cylinder with an upper porous sidewall and an inner cylindrical column. Porous- surfaced bodies constitute an important class of maritime structures since they can reduce the influence of wave-body interaction through pores on the body surface. Thus, a porous sidewall surrounding an inner column of a truncated cylindrical body can be used to effectively reduce both the transmitted and reflected wave trains. In past decades, numerous works have been presented concerning the behavior of porous bodies in waves. To raise some of them as examples, Teng et al., (2001) studied the wave diffraction from a bottom seated cylinder with porous upper wall and an inner column, whereas Ning et al., (2017) extended the previous work for a floating truncated cylinder with an upper sidewall. Other similar studies on concentric porous cylinder systems are those from Wang & Ren, (1994); Song & Tao, (2007); Liu et al., (2018).