Feng, Y., Feng, Y., Han, K., Owen, D., & Owen, R. (2012). Energy-conserving contact interaction models for arbitrarily shaped discrete elements. Computer Methods in Applied Mechanics and Engineering, 205-208, pp. 169-177. doi:10.1016/j.cma.2011.02.010

Feng, Yuntian, Y.T Feng, K. Han, D.R.J Owen, and Roger Owen. "Energy-conserving Contact Interaction Models for Arbitrarily Shaped Discrete Elements." Computer Methods in Applied Mechanics and Engineering 205-208 (2012): 169-177.

Feng, Yuntian, et al. "Energy-conserving Contact Interaction Models for Arbitrarily Shaped Discrete Elements." Computer Methods in Applied Mechanics and Engineering 205-208 (2012): 169-177.