When you simulate something, you imitate it. Hollywood makeup artists can use pencils and gray wigs to simulate old age in a young actor. It can also mean to model — a computer can simulate disaster scenarios in cities.
If you really admire someone's calm-under-pressure attitude, you may try to simulate their demeanor. When opening a present, it's polite to simulate surprise and excitement about the gift item, even if you already have it or it is ugly as dirt. Don't try to simulate your parents' signatures on excuse cards, though — signatures are unique to individuals and impossible to simulate perfectly.