Vortex-induced vibrations (VIV) are generally evaluated with relatively simpler two-dimensional (2D) methods using direct numerical simulation (DNS), large eddy simulation (LES) or RANSE-based (Reynolds-Averaged Navier-Stokes Equations) methods. Computationally, these 2D approaches have relatively lower costs which make them more suitable for such applications. However, 2D flow assumes that there are no tip-flows at both ends or no cross-flows along the moving body. Cellular shedding, which also adds three-dimensionality in VIV, is also neglected. This study proposes a simpler 2D computational approach that accounts for the three-dimensional (3D) flow for VIV. A three-dimensionality factor is introduced to the forced vibration equation which allows calibration of numerical solutions with experiments. Numerical model presented in this study is developed for practical engineering approaches and takes all three dimensional effects into account. The model is tested with two different experimental setups. The first one is with the experiments carried out at the Ata Nutku Ship Model Testing Laboratory and the second is with the experiments published in the literature. Results of this study show that as the effects of tip flow, cellular shedding and cross-flows increase, range of synchronization decreases. The other outcome of this study is that the method adopted in this paper can be used to enhance numerical simulations of vibrating bodies in fluids.