| 摘要 |
A seismic source (10) is described which drives one or more jets of high velocity water into an underwater environment and then abruptly terminates the jets. The momentum of the free jet columns generate vapor cavities in the water away from the housing (12) of the source which cavities collapse coherently to generate the seismic signal. A piston (22) and a valve sleeve (38) are slidably mounted in a cylinder (14) in the housing. The piston seals off a volume of gas on its rearward side. The forward side of the piston defines one surface of a chamber (24). The chamber receives high pressure water from an inlet. In its rearward position the valve sleeve seals a set of jet apertures (60) in the side of the cylinder. In its forward position the valve sleeve opens the apertures, exposing the chamber interior to the exterior underwater environment. With the valve sleeve in its rearward position with the apertures sealed, the high pressure water entering the chamber (24) moves the piston to its rearward position and compresses the gas. The sleeve (38) is hydraulically actuated upon command to abruptly open the jet apertures, enabling the piston to move forwardly under the pressure of the compressed gas, driving the water through the jet apertures so as to form the jets. The piston (22) enters the interior (40) of the sleeve (38) near the forward end of its stroke and, concurrently, abruptly terminates the jets. To re-arm the source, the sleeve is actuated to close the jet openings whereupon the high pressure water resets the piston (22). Upon the next command, the valve sleeve (38) is again actuated to open the apertures and the next seismic signal is generated. |
