Numerical Simulation Of Hydrodynamic Interactions Between Two Ships In Underway Replenishment At Sea

To meet the need of improving ships' survivability and endurance to enhance the ability of comprehensive and rapid replenishment at sea (RAS), many new requirements on underway replenishment at sea are brought forward, such as refueling at the specified time and in the best replenishment point, and multi-direction three-dimensional replenishment at high sea state. As an important step of the maritime logistics, underway replenishment at sea has been brought more and more attention of navies in the world and the ship-building architects. The hydrodynamic forces on both ships in underway replenishment at sea are diflFerent from those on single ship moving in the waves, one of which will affect not only by the disturbance of the neighboring ship, but also the sheltering effect. Therefore one of the keys of the theoretical research on RAS mainly focuses on studying the hydrodynamic interaction effect between two ships. In this paper, the problem will be deeply studied, aiming to present some technique instruction for the best choice of separation distances, forward speeds of two ships and wave headings. The main contents of this paper are:1. Based on the potential flow theory, 2D strip theory (STF) is adopted to study the hydrodynamic interaction effect between two ships moving in the waves. A frigate and a supply ship are selected for numerical simulation of the five freedom-degree motions of each ship.2. On the basis of the 3D potential flow theory, the interaction effects due to the coupled motions and hydrodynamic forces of two ships with forward speed in waves are computed by the 3D panel method based on the zero forward speed free-surface Green function with a forward speed correction. To verify the code, two identical cylinders are selected for numerical calculation of hydrodynamic interactions in water of finite depth in beam waves. Furthermore, two ship interactions in deep water are carried out in head waves with or without forward speed. The separation distance effect on interactions has also been studied.3. Based on 3D frequency theory, the spectral analysis method is used to predict the significant amplitudes of the relative motions between two ships on loading point. An efficient method of best choice for the forward speeds and lateral clearances atdifferent sea states and heading waves is presented for the need of the underway replenishment at sea. The numerical calculation on a supply ship and a frigate ship is carried out, and some theoretical instructions are presented for the choice of the speeds and the separation distances between two ships.4. On the basis of the 3D potential flow theory, the integral and differential methods are adopted to predict 2nd-order stable forces and moments of single and two submerged bodies advancing in the waves. Moreover the integral method is adopted to study 2nd-order stable forces and moments of single and two floating bodies in waves. The effect of the lateral distance between two ships on the 2nd-order lateral drift force and stable yaw moment is considered in detail, which will help to the verification of the lateral distance between two ships.5. As an initiating work, the hydrodynamic interactions between two ships without flare are studied based on the 3D time domain theory. The numerical results are compared with those of 3D frequency method and the speed effect is considered. On the basis of the spectral analysis method, the effect of wave headings on hydrodynamic interactions of two ships with different sizes in irregular waves is considered.6. Based on the potential flow theory, the interaction effects of two bodies moving in the unbounded fluid are studied with distributing simple source strength on the body surfaces. The sensitivity of stable force to grid number and calculation precision of the method based on the simplified body boundary condition are studied in detail. Moreover, the interaction effect of two floating bodies with same forward speed in the static water is studied without and with considering the free-surface effect. The speed and separation distance effect on stable interaction force are considered. Based on the viscosity flow theory, CFD is used to calculate the viscous interaction effect of two ships moving in the static water on the basis of the module of double body flow (DBF).