The oblique water entry of a cylinder is investigated experimentally in the present study. The cylinder is driven by a computer-controlled linear motor to ensure the constant impact velocity during the water entry process. To investigate the influence of wave on the impact loads and cavity evolution, a special apparatus is designed which could conduct oblique water entry at arbitrary angles with a progressive wave. With an internal force sensor mounted inside the cylinder, the time history of impact force is recorded during the water entry. The cavity and splash induced by the impact are recorded by the high-speed cameras. To improve the accuracy of experimental results, a synchronous system is developed between the linear motor, force sensor measurement system, and high-speed cameras. The experimental results show that due to the change of entry positions at different phases of a progressive wave, the impact loads reveal a different dynamics behaviour.
The water entry problem has been studied for over a century. Due to its wide application, it is still of interest in the fields of hydrodynamics and ocean engineering. The impact load during the process of water entry is characterized by its high local pressure and short duration, which will threaten the safety and integrity of a structure. For this reason, the prediction of impact loads is a central design scenario for naval and offshore structures, ships even aerospace structures.
Because of the short duration of slamming stage, commonly the fluid is assumed to be incompressible and inviscid for convenient to study. The original theoretical work of impact loads is conducted by Von Karman (1929) motivated by investigating the landing of a seaplane. Based on the conservation of momentum, Von Karman derived a formula to predict the impact force. Wagner (1932) proposed a refined theory to predict the impact loads later, which includes the effect of pile-up water on the impact force. After that, Wagner's theory was further developed by many researchers to predict the impact loads more accurately. For example, Zhao and Faltinsen (1993), Korobkin (2005) and Oliver (2007).