Predictions of Ship Extreme Hydroelastic Load Responses in Harsh Irregular Waves and Hull Girder Ultimate Strength Assessment

Abstract

In this paper, the hydroelastic motion and load responses of a large flexible ship sailing in irregular seaways are predicted and the hull girder ultimate strength is subsequently evaluated. A three-dimensional time-domain nonlinear hydroelasticity theory is developed where the included nonlinearities are those arising from incident wave force, hydrostatic restoring force and slamming loads. The hull girder structure is simplified as a slender Timoshenko beam and fully coupled with the hydrodynamic model in a time domain. Segmented model towing-tank tests are then conducted to validate the proposed hydroelasticity theory. In addition, short-term and long-term predictions of ship responses in irregular seaways are conducted with the help of the developed hydroelastic code in order to determine the extreme design loads. Finally, a simplified strength-check equation is proposed, which will provide significant reference and convenience for ship design and evaluation. The hull girder ultimate strength is assessed by both the improved Rule approach and direct calculation.

Springing Analysis of a Passenger Ship in Waves

“…However, the total influence of springing on local stress tensors has not been evaluated. In addition, it is believed that hydroelasticity may have severe influence if the analysis is conducted on confined and detailed portions of the vessel in extreme waves where nonlinear hydrodynamic effects and impact loads may also be significant [22,46]. Accordingly, future work could concentrate more on understanding the combined influence of nonlinear hydrodynamic effects such as large amplitude motions, local slamming loads, and hull whipping on both global and local ship dynamics and strength over a broad range of passenger ship designs.…”

“…For example, Rajendran et al [20] confirmed the significant effects of bow flare variation on the rigid response of a bulker, a container ship and a passenger ship sailing in extreme waves and irregular seaways. Kim and Kim [21] and Jiao et al [22] predicted extreme loads by time-domain hydroelastic methods. Their work shows that: (a) the combination of rigid and flexible ship dynamics may influence the long-term vertical sagging and hogging moments amidships and (b) Classification Society Rules for ultimate strength assessment may be dependent on sea state variations and the associated cycle times of alternate loads.…”

Fully 3D ship hydroelasticity: Monolithic versus partitioned strategies for tight coupling

“…In this method, the evaluation of the vibration modes cannot be estimated properly in fully elastic models due to larger internal damping [5]. The second one (and the most popular) is to build a segmented model connected by a flexible beam with similar global elastic properties [2,6,7,8,9,10,11]. The number of segments depend on the number of displacement modes to model.…”

“…The numerical simulation of hydroelasticity involve the coupling between the hydrodynamics and the structural dynamics. The most common approach is to solve the hydrodynamics with 3D potential flow using the boundary element method (BEM), and the structural dynamics with the 1D beam model using the finite element method (FEM) [10,11,12,13,14,18]. Several works have extended the fluid dynamics model, by solving the Navier Stokes equations instead of the potential flow equations [15,16,17].…”

“…In order to be able to simulate transient or non-linear responses, it is necessary to work in the time-domain [1]. In the context of potential flow solvers, Cummins [20] proposed the use of the impulse response function to transfer the results from the frequency-domain to the timedomain, and different authors have followed this approach [9,10,11,18]. It requires to perform the structural modal analysis, and to solve the wave radiation problem for the corresponding displacement modes.…”