The U.S. stock market has been strangely calm this year, much to the chagrin of investors who have been betting billions on volatility. The CBOE Volatility Index, or VIX, is down about 30 percent year-to-date, even though some investors have been expecting a rockier stock market as the Federal Reserve gets ready to raise interest rates and the six-year-old bull market ages. “Right now volatility is at that level because no one is talking in panic terms,” said Andrew Wilkinson, chief market analyst at Interactive Brokers Group in Greenwich, Connecticut.