Collision between ship and pier will not only cause damage to pier or hull structure, but also cause catastrophic consequences such as casualties and environmental pollution. Therefore, the effective anti-collision design is installed on the pier fender To absorb the impact energy, reduce the collision force between ship and bridge, and improve the safety of ship and bridge, it has important practical significance. Scholars at home and abroad have done a lot of research on anti-collision fenders, and have achieved certain results in theoretical mechanism, numerical simulation, test methods, optimization design, etc.
The composite anti-collision fenders are attracting more and more attention due to their advantages such as light weight, corrosion resistance, stronger energy absorption capacity and more uniform distribution of crushing load. However, at present, the optimization design of composite anti-collision fenders is rarely involved. For this reason, this paper takes composite anti-collision fenders as the research object, and optimizes the structure of circular composite anti-collision fenders on the ANSYS/LS-DYNA and Isight platforms, providing a basis for the selection of structural parameters.
Collision design standard of anti-collision fender
In order to obtain the allowable value of the maximum collision force after the anti-collision fender is installed, it is necessary to first calculate the maximum collision force of bridge collision when the anti-collision fender is not installed. There are many factors that affect the collision force of ship bridge, and the theoretical calculation is very complicated. At present, different simplified formulas or specifications are used for calculation according to specific situations at home and abroad. The commonly used ones are AASHTO specifications, European specifications, China's highway specifications, China's railway specifications, and woisin correction formula. Each simplified formula has a certain scope of application.
According to the design requirements of inland waterways, the maximum collision force adopts the European code as the standard. When a 1000 ton ship collides with the bridge at a speed of 3.9m/s, the maximum collision force is 30.2MN. After the annular composite anti-collision fender is installed, the allowable value of its collision force is "maximum collision force (MN)" × 52.4%, that is, after the anti-collision fenders are installed on the inland waterway bridges, the maximum collision force of the bridge for 1000 ton ships should not exceed 15.82MN.
Comparison of crash test and finite element calculation results
In this paper, the finite element method is used to simulate the collision process between a 1000 ton cargo ship and a bridge, and then the structure of the annular composite anti-collision fender is optimized. The accuracy of the finite element model needs to be verified by comparing the test results. Due to the difficulty of ship bridge collision test, this paper first conducts drop hammer impact test on composite anti-collision fender samples, and uses finite element method to simulate the process of drop hammer test. Through the comparison of the results, the selection principles of the material properties and element types of the annular composite anti-collision fender are determined, which lays the foundation for obtaining the relatively accurate finite element model of the anti-collision fender.
The annular composite anti-collision fender shell and energy dissipation plate are made of glass fiber board, supported by glass fiber core column inside, and filled with polyurethane foam inside the structure as energy dissipation material. This combination of materials and structures can not only maximize the energy absorption effect, but also avoid large-scale damage caused by impact on the structure. Make test samples according to this structure, and simulate the ship bridge collision through the drop hammer impact test. First, place the fabricated specimen on the rigid table in the environmental box, and then use a hemispherical hammer with a diameter of 25.4mm to impact the surface of the specimen at low speed on the drop hammer impact tester CEAST9350. The test results are in good agreement with the results of the ANSYS/LS-DYNA numerical simulation, which shows that the ANSYS/LS-DYNA simulation is reliable enough to calculate the collision dynamic characteristics of the annular composite fender.
Collision simulation
1. Structural type of anti-collision fender
The design of anti-collision fender shall follow the principle of not obstructing the channel, so the size of anti-collision fender shall be minimized as far as possible under the condition of ensuring anti-collision performance. This paper mainly carries out anti-collision design for 1000 ton ships in inland waterways. According to the calculation and the size of the bridge, the outer ring diameter is determined as the outer ring size Φ 2500mm, inner ring diameter Φ 1500mm。 The glass fiber core columns are evenly distributed, and the position of the energy dissipation plate is determined by its diameter. Because its diameter has a certain impact on the energy dissipation effect of the anti-collision fender, this paper takes it as a design variable to determine its exact position after optimization. The section form of the toroidal anti-collision fender is shown in Figure 1. In order to facilitate installation and replacement, the designed anti-collision fender structure is assembled by sections with a length of 6m. The whole anti-collision fender is installed around the pier
2. Finite element simulation of collision between ship and anti-collision fender
In the process of numerical simulation of ship bridge collision, it is very important to establish an accurate finite element model, but due to the complexity of collision, it is often impossible to establish a finite element model according to the actual structure. Therefore, the model is simplified to meet the strength requirements of the ship. In this paper, the bridge collision simulation is carried out for a 1000 ton bulk carrier. The model structure is established according to the actual hull structure size. The main parameters of the ship are shown in Table 1. The whole hull uses shell units. The finite element model of anti-collision fender is established according to the change of design structure. The fender plate uses shell element, the core column uses beam element, and the foam material uses solid element. Because the collision contact occurs locally, the collision damage also occurs locally. In order to improve the simulation speed, the simulation model of the anti-collision fender is simplified as a part installed on the pier. However, due to the large rigidity of the pier, the small deformation in the collision process, and the small impact on the ship and bridge, the finite element model of the pier is omitted. In the calculation, add constraints to the contact part between the anti-collision fender and the pier to control. Since the fender and the pier are flexible connections, the maximum collision force between the fender and the pier is not greater than the maximum collision force of the ship fender collision.
After setting the element type, material properties, contact algorithm and adding constraint control, the finite element simulation of the collision process of the bridge is carried out. Figure 4 shows that the thickness of the crash fender energy dissipation plate and the diameter of the core column are both 3mm, and the diameter of the energy dissipation plate is Φ According to the numerical simulation results at 1800 mm, the collision force on the way is the maximum collision force of ship fender collision.
