The pilot reported that during the landing flare, he was startled by the early impact and bounce. The airplane touched down hard and bounced about three times in a "porpoise pattern." He increased power to abort the landing, and he retracted the flaps but, "It was too late to recover." He reduced engine power and the airplane rolled to a stop on the runway. The airplane sustained substantial damage to the lower fuselage bulkhead. The airport's METAR reported that about the time of the accident, the wind was from 210° at 5 knots. The airplane landed on runway 04L. The airport elevation was 618ft, the temperature was 82°F, the barometric setting was 29.94, and the estimated density altitude was 2,300ft. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.