One of the most important steps in the hydrodynamic analysis of surface vessels or underwater vehicles is determination of fluid resistance. This step achieved by performing resistance tests in a towing tank or using numerical methods. In this research the resistance and the wave profile around the Caspian3 surface vessel hull, constructed by KEPCO Company, is experimentally and numerically investigated. Caspian3 is one of the largest supply vessels in Iran. The main application of supply vessel is to transfer the drilling rigs. One of the main characteristics of the Caspian3 is its moonpool. Moonpool is a wetted opening, located near the midship, and allows researchers to take their vehicles and tools into the water in a safer circumstance. The effect of moonpool on the vehicle resistance at various Froude number in the range of 0.139-0.370 is studied by performing a set of experiments in the subsea R D towing tank of Isfahan University of Technology (IUT) and using numerical commercial Ansys-CFX code. The towing tank of IUT has a length of 108 meters, width of 2 meters and a depth of 2.2 meters. A 1:37.2 scaled model with a length of 2 meters, width of 0.47 meter and a draft of 0.17 meters is fabricated to perform the experiments based on ITTC procedures. The experimental results obtained agreed well with those obtained by HSVA towing tank, using a 1:17.2 scaled model. HSVA is one of the most well equipped ITTC members. The experiments with this model, in HSVA, were carried out in 2010. During the IUT tests a dynamometer is used to measure the forces and torques in 3 directions. The model is filled with sufficient lead blocks, in order to obtain a draft corresponding to the real vessel draft. The wave profiles around the hull vessel for various Froude number are also investigated. Using a video camera the wave profile is captured at various Froude numbers. In the numerical part of the present work, a two phase flow model is used to simulate the steady state motion of the vessel. The domain is consisted of water and air fluids, separated by a free surface. An unstructured mesh around the ship hull used. A boundary layer around the hull surface, as well as, the moon pool peripheral walls is considered, in order to obtain more accurate results. A larger number of meshes at the free surface and around the hull are used to achieve convergences and to obtain accurate results. A k-? turbulent model is used in the numerical study. The Contours of volume fraction obtained from the numerical simulations, indicating the flow structure around the hull, agree well with the wave profile observed during experimental results. All experimental and numerical studies are carried out for both open and closed moonpool. The results obtained for the resistance using experimental and numerical method for open and closed moonpool differ up to 6 percent. The numerical and experimental results show that the total resistance of the ship with open moonpool is 21% larger than that of closed moon pool. Key words Resistance test; Towing tank; ITTC; moonpool ; Ansys-CFX
