The;
First;
Fundamental;
Department,;
Beijing;
Information;
Technology;
Institute,;
Beijing;
100101,;
China;
Institute;
of;
Computational;
Mathematics;
and;
Scientific/Engineering;
Computing,;
Academy;
of;
Mathe;
matics;
and;
System;
Sciences,;
Chinese;
Academy;
of;
Sciences,;
Beijing;
100080,;
China;
unilateral; contact; problem,; mixed; finite; element; method.;