en Numerical Investigation مقاله پژوهشي Research Paper <span style="font-size:11.0pt"><span new="" roman="" style="font-family:" times="">The aim of the present study is calculation of the resistance and resistance coefficient of a diver on the water surface and near surface. The results of this article are useful for designing different types of water scooters. This study uses a computational fluid dynamics methodology by considering the effects of free surface. SST K-&omega; turbulent model is implemented in the Star-CCM+ application and is applied to the flow around a three-dimensional bare hull of an adult human. Three common swimming positions are considered: a ventral position with the arms extended at the front, a ventral position with the arms placed alongside the trunk and a ventral position with one arm extended at the front and another arm placed alongside the trunk. The flow velocities between 0.5 and 2.25m/s with increasing step of 0.25m/s are considered in the simulations which are typical speed of swimmers. According to the resistance coefficient vs Froude number diagrams, submerged diving with two hands alongside the trunk is produces lower resistance. Also, resistance in near surface swimming is lower than surface swimming in lowest speeds. But in higher speeds, that changes and resistance in surface swimming is lower than the other. The results of this research can be used for designing all types of marine propulsion vehicles, water scooter, and all swimming thrusters. </span></span> human body,diver resistance,swimmer resistance,CFD,resistance coefficient,free surface simulation 15 24 http://ijmt.ir/browse.php?a_code=A-10-7426-1&slc_lang=en&sid=1 Nima Khanmoradi nimakhanmoradi.edu@gmail.com 10031947532846004067 10031947532846004067 Yes Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran. Mohammad Moonesun m.moonesun@gmail.com 10031947532846004068 10031947532846004068 No 2Department of Civil & Architectural Engineering, Shahrood University, Shahrood, Iran. Sara Jafari Horestani sara1995jafari@gmail.com 10031947532846004069 10031947532846004069 No Department of Physical Education and Sport Sciences, Kharazmi University, Tehran, Iran.