Pressure Variation on Shallow Water Bottom caused by Moving Ship

The pressure variation on shallow water bottom caused by a moving ship is of vital importance for safety. In this paper,the similarity method of the experiment about hydrodynamic pressure field is studied, and a conversion formula about hydrodynamic pressure field between the ship model and the full scale ship is presented. the A pressure measurement system with high precision was established, and the experiment of the measurement of ships hydrodynamic pressure field on water bottom was carried out in the model tank. The change laws of the pressure field are summarized systematically. The influence factors of suction pressure peak are analyzed. The change along ship length of the dynamic pressure coefficient is obtained. In the case of subcritical speed, relatively large barotropic sections appear near the bow and the stern, but on most mid ship sections the pressure coefficient is negative. As depth Froude number increases, negative pressure coefficient peak will move to the stern, even may move behind the stern in the range of supercritical speed. Applying the slender ship theory in shallow water, a calculation formula of hydrodynamic pressure field is deduced and simplified by ignoring nonliear effect. For supercritical speed, the calculated pressure field on the water bottom induced by an advancing ship indicates that the pressure distribution takes a V shape wave pattern at the bow and the stern. The larger depth Froude number is, the smaller V shape angle is, namely the pressure distribution spreading along transverse direction has a narrower range. For subcritical speed, the calculated longitudinal passing characteristic curves of the pressure field indicate that negative pressure distribution takes the W shape wave pattern under the ship. As the water depth or the ship speed increases, the negative pressure under the ship will turns into V shape distribution. The slender ship theory in shallow water was also applied to calculating the negative pressure coefficient peak on the water bottom caused by an advancing ship, the calculated results are in good accordance with measured values, in most of the speed region but a relatively large deviation exists near the critical speed.