A Crashworthy Device Against Ship-OWT Collision and Its Protection Effects on the Tower of Offshore Wind Farms

At present, more and more offshore wind farms have been built anti ntnnerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines （OWT） is of great practical signifieance. The present study takes the advantage of the famous LS-DYNA explicit code to simulate the dynamic proeess of the collision between a typical 3MW offshore wind turbine model with monopile fi）undation and a simplified 2000t-class ship model. In the simulation, the added mass effect of the ship, contact nonlinearity of collision, material nonlinearity of steel and aluminum foam and adaptive mesh tectmique for large structure deformation have been taken into considera- tion. Proposed is a crashworthy device for OWF of new conceptual steel sphere shell-cireular ring aluminum foam pad, and the good pe.rfurmanee of the device under the conditions of ship-OWT front impact and side impact has been verified from the views of theoretical analysis and numerical results. The new crashworthy device can effectively smooth the contact force and reduce the top structure dynamic response, using its own structure plastic deformation to absorb most of the ship collision enerty. As a result, the main structure of the OWF and the inside key electric control equipments can be saved by scarifying the structural plastic deformation of new sphere crashworthy device. What is more, the sphere configuratiun design of the crashworthy device can effectively guide the ship to run away from the main OWT structure and reduce the damage of the ship and OWT to some degree during side impact.

Dynamic Simulation on Collision Between Ship and Offshore Wind Turbine

By using ABAQUS/Explicit, the dynamic process of an offshore wind turbine(OWT) stricken by a ship of 5000DWT in the front direction is simulated. The OWT is located on a large-scale prestressing bucket foundation constructed by an integrated installation technique. According to the simulation results, under the ship collision, a certain range of plastic zone appears within a local area of arc transition structure of the bucket foundation, and the concrete plastic zone is seriously damaged. As the stress level of OWT tower is relatively low, the OWT tower is less affected. A great inertial force is generated at the top of the OWT tower as the mass of nacelle and blades is up to 400 t. The displacement of the tower is in the opposite direction of the ship collision at the end of 1 s under the action of inertial force. There is only a minor damage in the ship bow. Most of the kinetic energy is transformed into the plastic dissipation and absorbed by the arc transition structure of bucket foundation.

Study on Collision Between Two Ships Using Selected Parameters in Collision Simulation

In the present analysis, several parameters used in a numerical simulation are investigated in an integrated study to obtain their influence on the process and results of this simulation. The parameters studied are element formulation, friction coefficient, and material model. Numerical simulations using the non-linear finite element method are conducted to produce virtual experimental data for several collision scenarios. Pattern and size damages caused by collision in a real accident case are assumed as real experimental data, and these are used to validate the method. The element model study performed indicates that the Belytschko-Tsay element formulation should be recommended for use in virtual experiments. It is recommended that the real value of the friction coefficient for materials involved is applied in simulations. For the study of the material model, the application of materials with high yield strength is recommended for use in the side hull structure.

Critical Void Volume Fraction Identification Based on Mesoscopic Damage Model for NVA Shipbuilding Steel

NVA mild steel is a commonly used material in the shipbuilding industry.An accurate model for description of this material’s ductile fracture behaviour in numerical simulation is still a challenging task.In this paper,a new method for predicting the critical void volume fraction fc in the Guson-Tvergaard-Needleman(GTN)model is introduced to describe the ductile fracture behaviour of NVA shipbuilding mild steel during ship collision and grounding scenarios.Most of the previous methods for determination of the parameter fc use a converse method,which determines the values of the parameters through comparisons between experi-mental results and numerical simulation results but with high uncertainty.A new method is proposed based on the Hill,Bressan,and Williams hypothesis,which reduces the uncertainty to a satisfying extent.To accurately describe the stress-strain relationship of materials before and after necking,a combination of the Voce and Swift models is used to describe the material properties of NVA mild steel.A user-defined material subroutine has been developed to enable the application of the new parameter deter-mination method and its implementation in the finite element software LS-DYNA.It is observed that the model can accurately describe structural damage by comparing the numerical simulation results with those of experiments;thus,the results demon-strate the model’s capacity for structural response prediction in ship collision and grounding scenario simulations。

Composition ship collision risk based on fuzzy theory

Despite of modern navigation devices, there are problems in navigation of vessels in waterways due to the geographical structures, disturbances in water, dynamic nature, and heavily environmental influenced sea traffic. Even though all vessels are equipped with modern navigation devices, the accidents are reported caused by various reasons and mainly by human factor according to investigation. We propose an effective and efficient composition collision risk calculation method for finding the collision probability and avoiding the collision between ships in possible collision situations. The proposed composition collision risk calculation method at ship's position using combination of fuzzy and fuzzy comprehensive evaluation methods. The algorithm is straightforward to implement and is shown to be effective in automatic ship handling for ships involved in complex navigation situations. Experiments are carried out with indigenous data and the results show the effectiveness of the proposed approach.

Simulation and Reasonable Design of Bridge Steel Fenders to Reduce Ship Impacts

Steel fenders are increasingly used for ship-impact resistance structures in the design of navigable bridges. As an important approach to investigating this anti-impact structure effectiveness to reduce influences of vessel impact, simulation analyses are still not perfect yet. So this paper is intended to discuss several issues related to ship collision simulations, including steel constitutive relationship, connections between steel box and pile cap, contacts definition and friction consideration, and the determination of impact waterlines and angles. Consequently based on two examples of ship-steel fender-bridge structure systems, some conclusions about effectiveness and design of fenders to reduce ship impact are drawn.

Application of Viscoelastic Materials in Ship Collision

With the expansion of global trade routes,ship collision has become a major problem.This article proposes an approach by laying viscoelastic material on the inner side of the ship to increase the crashworthiness.By using the nonlinear finite element model software,this study simulates ship collisions as well as models and analyzes ships along with viscoelastic materials.The results from the simulation suggest that viscoelastic materials can effectively protect ships during collisions.

Effects of Introducing Ship Handling Training for Collision Avoidance in Anchoring Training-Effects of Ship Handling Training for Collision Avoidance by Group Work

In shipping,which is one of the drivers of the world’s economy,many marine accidents continue to occur,such as ship collisions and grounding.To reduce marine collision accidents,seafarers’skills must be improved through training.Therefore,the authors propose a ship handling training for collision avoidance(hereinafter referred to as“T for CA”)in which a group of several people discusses the ship handling for collision avoidance,assuming the situation of the collision avoidance.After T for CA implementation,anchoring training was done and the effect of T for CA was verified through comparison with a group where T for CA was not applied.Two instructors evaluated the anchoring training conducted with and without“T for CA”.The anchoring training experiment showed a difference of 27.5%in the achievement rate between the proposed training and previous training.T for CA maximises the effects of group work and resulted in good evaluations in the anchoring training experiments.The training was effective because the students themselves set the scenarios and devised ship handling strategies for collision avoidance.In addition,group work discussions helped deepen students’knowledge and skills.

考虑到船舶机动性和会遇情况的一种新的面向船舶领域的船舶碰撞风险参数

The identification of ship collision risks is an important element in maritime safety and management.The concept of the ship domain has also been studied and developed since it was proposed.Considering the existing trend that the ship domain is increasingly widely used in collision risk-related research,a new domain-oriented collision risk factor,i.e.,the current state of domain(CSD),is introduced in this paper,which can effectively reflect the current state and show a certain predictability of collision risk from the perspective of the ship domain.To further prove the rationality of the CSD,a series of different simulations consisting of three typical encounter scenarios were conducted,verifying the superiority of the proposed parameter.

Dynamic response analysis of ship-bridge collisions experiment

Over the past decades, there has been continual construction of sea-crossing bridges as the technology of transportation improves. The probability of bridge pier being subjected to more vehicular impact is also growing. This study performed scale model tests and analyzed a collision mechanism considering the non-navigable span of a sea-crossing bridge in East China Sea as an engineering background. Comparing the test results with the finite element calculations, the dynamic response of the sample bridge and local damages of the fragile components under impact force were evaluated. Subsequently, the time-frequency characteristics of the vibration signal were analyzed based on wavelet packet analysis, and the multi-resolution characteristics as well as energy distribution of the vibration signal were discussed. It was observed that the impact energy transferred from ship to pier during the period of collision distributed different frequency bands with varying characteristics. The main frequency band(0–62.5 Hz) contains more than 75% of the vibration energy. The analysis can provide a basis for structural damage identification after the collision and anti-collision design of bridges.

Challenges and Innovations in the Sutong Bridge Foundation Project

This article introduces three outstanding innovations, i.e. utilization of the steel casing for the piles to establish a construction platform for Sutong Bridge's large and deep-pile groups; 5000 ton steel cofferdam lowered as a whole and used as a protective structure against impact from ship collision; Permanent scour protection. This article also presents economical and reasonable design method for large bridge foundation and explains the significance of innovation and technical integration to large and complicated project construction based on the above theory.

Numerical analysis method of ship-ice collision-induced vibration of the polar transport vessel based on the full coupling of ship-ice-water-air

As the Arctic Channel continues to be developed,collisions between polar navigation vessels and sea ice are inevitable,which will directly affect structural safety and vibration comfort.However,the numerical analysis method of ship-ice collision-induced vibration is not perfect,and the effect of fluid coupling is not typically considered.In this paper,a simplified numerical analysis method for ship-ice collision-induced vibration is proposed,in which a reliable ice load is obtained by first performing ship-ice-water-air coupled collision calculations,followed by ship-ice-water coupled vibration calculations to obtain the vibration response of the structure.In addition,this paper investigates the full coupling method and the modeling ranges and meshing sizes involved in the analysis ship-ice collision-induced vibration,and the computational efficiencies of the traditional ALE algorithm and S-ALE algorithm are compared.The results indicate that the simplified simulation analysis method and gradient meshing model improve the calculation accuracy and efficiency in ship-ice collision and vibration response analysis.Moreover,the modeling range of the water and air models cannot be less than 6 times the ship width,2 times the ship length,and 1 times the ship depth,and the S-ALE algorithm saves 47.86%time compared to the ALE algorithm.The research results in this paper can provide a reference for the numerical simulation of ship-ice collision-induced vibration.

STUDY OF HYDRODYNAMIC FORCES OF SHIPS IN NARROW WATERWAY

The collision of ships in narrow waterway may occur for a variety of reasons.The hydrodynamic forces between two ships change the maneuvering characteristics of ships greatly.So based on the boundary element method, this paper proposes a calculation method for hydrodynamicinteraction forces between ships under meeting and passing conditions in narrow waterway. Theresults from this method are compared with the existing results obtained from other theoreticalapproaches, and they are in good agreement.

Deliberative Collision Avoidance for Unmanned Surface Vehicle Based on the Directional Weight

The purpose of this study is to realize the intelligent deliberative obstacle avoidance for unmanned surface vehicle(USV), based on the International Regulations for Preventing Collisions at Sea called COLREGS.Firstly, a three-level system architecture is designed for the ship intelligent collision avoidance system. Secondly,an intelligent collision avoidance algorithm is presented based on the calculation of motion parameters and the rules of COLREGS. Thirdly, according to COLREGS, the marine environment is modeled from the electronic chart data and radar information, and a deliberative collision avoidance algorithm is written. Finally, the deliberative collision avoidance simulation is carried out for the USV. The feasibility and reliability of intelligent collision avoidance algorithm are verified by the vivid simulation results.