Bats are the only mammals that can power their flight, and several species have adapted themselves to fly through complex and tight environments. Understanding the complex wing aerodynamics could provide unique design ideas for Bio-inspired micro-aerial vehicles. A bat's hand wing is formed from a very thin and highly elastic membrane reinforced by the bones known as digits. The fluid-structure interaction (FSI) between the flapping wing and airflow generates the aerodynamic forces that support the bat's flight. This work attempts to model the complex FSI and understand the aerodynamics by developing a numerical simulation model using experimental data of a bat in forward flight. The direct numerical fluid flow simulations were performed using our in-house sharp-interface immersed boundary code, ViCar3D. The structural deformations are commonly modeled using the finite-element method. However, the large deformations in the bat's wing require a complex computational infrastructure which could tremendously add to the computational cost of performing these simulations. We used a spring network model for aeroelastic deformation in flexible membrane wings. These methods were initially developed for rapid simulation of cloth in computer animations, and they were also successful in performing FSI simulations of heart valves, red blood cells, membrane parachutes, etc., at low computational costs. Here the membrane dynamics is modeled by solving multiple spring-mass-damper systems that control the in-plane and out-of-plane deformations. The aerodynamic forces in such flights depend upon different mechanisms like the role of vortices, added-mass effects, flow acceleration in the free stream, and viscous diffusion. The decomposition of lift and thrust forces into these different contributions could provide insights into the complex fluid dynamics involved in such FSI problems. This was done using the Force Partitioning Method (FPM). FPM revealed that the high-frequency oscillation in these FSI problems is due to the added-mass effects associated with the flutter of the membrane. Further, the contribution of vortex-induced and added mass effects in different phases of the flight was also quantified. This research is supported by NSF Grant CBET-2011619.