Dynamic Response Of Ship Research Articles

Comparison of numerical approaches for structural response analysis of passenger ships in collisions and groundings

The dynamic response of ships following grounding and collision accidents may be influenced by structural topology as well as operational and environmental conditions. Traditionally, the consequences of such events may be assessed by crude empirical methods or laborious experiments. Computational methods offer a useful alternative in terms of accurately capturing crushing mechanisms also accounting the influence of surrounding water. This paper presents a benchmark study that compares the structural dynamic response by explicit nonlinear FEA approaches and the semi-numerical super-element method. Simulations for typical accident scenarios involving passenger ships confirm that implementing the influence of hydrodynamic restoring forces in way of contact may be useful for either collision or grounding. Yet, for grounding scenarios, the damaged area resulting from analytical simulations appears to be sensitive to the failure strain values adopted to model the rupture of the ship bottom floors.

Experimental and modelling study on the response of mooring container ships in port under medium to long period waves

For understanding the influence of medium to long period waves on the dynamic response of ships, the hydrodynamic analysis of three typical moored container ships under wave interaction is carried out based on potential flow theory. The calculated and experimental results comparison shows that the numerical calculation is more suitable for simulation of long-period wave, as the dynamic response of ship is larger, but more accurate. For the larger ship, the peak response period of the mooring system usually reaches 100 s because the mooring stiffness is relatively small. With extended wave period, the ship motion response increases almost linearly. The symmetrical mooring arrangement and the similar mooring stiffness can effectively reduce the inhomogeneity of mooring forces. In addition, the ship motion and mooring force response can reach a minimum value at a special angle between ship and wave.

Experimental and modelling study on the response of mooring container ships in port under medium to long period waves

For understanding the influence of medium to long period waves on the dynamic response of ships, the hydrodynamic analysis of three typical moored container ships under wave interaction is carried out based on potential flow theory. The calculated and experimental results comparison shows that the numerical calculation is more suitable for simulation of long-period wave, as the dynamic response of ship is larger, but more accurate. For the larger ship, the peak response period of the mooring system usually reaches 100 s because the mooring stiffness is relatively small. With extended wave period, the ship motion response increases almost linearly. The symmetrical mooring arrangement and the similar mooring stiffness can effectively reduce the inhomogeneity of mooring forces. In addition, the ship motion and mooring force response can reach a minimum value at a special angle between ship and wave.

A Two-Dimensional Hydroelastoplasticity Method of a Container Ship in Extreme Waves

Extreme waves have led to many accidents and losses of ships at sea. In this paper, a two-dimensional (2D) hydroelastoplasticity method is proposed as a means of studying the nonlinear dynamic response of a container ship when traversing extreme waves, while considering the ultimate strength of the ship. On one hand, traditional ultimate strength evaluations are undertaken by making a quasi-static assumption and the dynamic wave effect is not considered. On the other hand, the dynamic response of a ship as induced by a wave is studied on the basis of the hydroelasticity theory so that the nonlinear structural response of the ship cannot be obtained for large waves. Therefore, a 2D hydroelastoplasticity method, which takes the coupling between time-domain waves and the nonlinear ship beam into account, is proposed. This method is based on an hydroelasticity method and a simplified progressive collapse method that combines the wave load and the structural nonlinearity. A simplified progressive collapse method, which considers the plastic nonlinearity and buckling effect of stiffened, is used to calculate the ultimate strength and nonlinear relationship between the bending moment and curvature, so that the nonlinear relationship between the rigidity and curvature is also obtained. A dynamic reduction in rigidity related to deformation could influence the strength and curvature of a ship's beam; therefore, it is input into a dynamic hydrodynamic formula rather than being regarded as a constant structural rigidity in a hydroelastic equation. A number of numerical extreme wave models are selected for computing the hydroelastoplasticity, such that large deformations occur and nonlinear dynamic vertical bending moment (VBM) is generated when the ship traverses these extreme waves. As the height and Froude number of these extreme waves are increased, a number of hydroelastoplasticity results including VBM and deformational curvature are computed and compared with results obtained with the hydroelasticity method, and then, some differences are observed and conclusions are drawn.

Prediction of shock-induced cavitation in water

Fluid-structure interaction problems that require estimating the response of thin structures within fluids to shock loading have wide applicability. For example, these problems may include underwater explosions and the dynamic response of ships and submarines; and biological applications such as Traumatic Brain Injury (TBI) and wound ballistics. In all of these applications the process of cavitation, where small cavities with dissolved gases or vapor are formed as the local pressure drops below the vapor pressure due to shock hydrodynamics, can cause significant damage to the surrounding thin structures or membranes if these bubbles collapse, generating additional shock loading. Hence, a two-phase equation of state (EOS) with three distinct regions of compression, expansion, and tension was developed to model shock-induced cavitation. This EOS was evaluated by comparing data from pressure and temperature shock Hugoniot measurements for water up to 400 kbar, and data from ultrasonic pressure measurements in tension to -0.3 kbar, to simulated responses from CTH, an Eulerian, finite volume shock code. The new EOS model showed significant improvement over preexisting CTH models such as the SESAME EOS for capturing cavitation.

Summary of the ISSC report of committee II. 2: dynamic load effects

Mandate concern for the dynamic response of ship and offshore structures as required for safety and serviceability assessments, including habitability. This should include steady state, transient and random response. Particular attention should be given to modelling accuracy

An Integrated Numerical Tools System For Marina Design

The Eureka EU 394 project is concerned with the development of a underwater wave attenuation system for nearshore protection. Wave breakers are composed of fixed or moored submerged horizontal flat plates. To optimize the efficiency of the breakers, numerical tools have been developed which analyse wave and current propagation and sediment transport from offshore to the coast. An extension of these tools has been performed to predict the wave fields inside marinas, induced wave loads on breakers and dynamic response of ships, pontoons and ro/ro systems. The paper mainly deals with the capabilities of these numerical tools.