Despite increasing popularity of compliant and underactuated hands, few tools are available for modeling them. Thus, we propose a simulation technique to predict the success of a compliant gripper grasping irregular objects, which could be used in mechanism design as well as grasp planning. The simulator we propose integrates joint compliance simulation with a Boundary Layer Expanded Mesh (BLEM) technique to enhance the stability of contact estimation. We compare the proposed simulator with existing simulators via a set of stability and fidelity criteria, including contact force variation, contact position variation, and contact normal variation. Scores along these criteria are correlated with the simulator's accuracy of predicting the success/failure of a given grasp pose and preshape. A test set of 13 grasps, with two compliant underactuated hands were manually generated on 4 objects. Experiments suggest that our simulator leads to improvements in the stability criteria, predictability of grasp success, and reduction of simulation artifacts.