Due to the effects of wind, waves and currents, as well as the driving skills of the driver, the ship generates different angle and speed forces on the front of the dock when berthing, and the forces under certain angle and speed combinations affect the fender and The pier has a greater destruction effect.
The cylindrical wharf is suspended at the front of the wharf and is only restricted by the upward pulling force of the iron chain and the vertical force of the wharf wall. If you think about the friction between the fender and the front wall of the wharf and the hull, it is also restricted by the force along the direction of the wharf wall. According to the material, currently used are rubber cylindrical fenders and polyurethane cylindrical fenders. Due to the small friction factor of the polyurethane fender (only 0.12), and the axis direction of the cylindrical fender along the direction of the pier wall, the shear damage caused by friction will not be great, so only the vertical contraction force needs to be considered Just fine.
As for the drum-type dock fender, due to its large volume, the vertical contraction amount is also large, so its energy absorption is very large in the existing fenders, but the defect is that it is vulnerable to lateral impact of the hull Since a large shear force is generated, it is necessary to consider the degree of stress. Due to the large volume of the ship and the fenders in accordance with certain rules, the drum pier fender is unlikely to withstand a degree of thrust, and it is mainly affected by shear forces such as side pressure and friction. .
Using finite element software to simulate and analyze the pressure condition of the fender, it can be known that the lateral displacement of the fender caused by the friction is greater than the pure tightening amount, but the force of the ship on the fender is that the volume pressure and the lateral friction stop at the same time, thinking about the fender The volume change after compaction and the lateral displacement caused by friction should be gradually reduced in proportion.
Judging from the current application status of the fenders, the cylindrical wharf fenders are difficult to meet the application requirements in terms of energy absorption; under normal docking conditions, the drum fenders can meet the application requirements in terms of energy absorption. To protect the drum fender from shear damage, a steel chain should be added to its proper position.
When selecting a wharf fender, the effective impact energy of the ship's berthing should be determined first. The absorption energy of the selected wharf when it is designed to shrink and deform should be greater than the effective impact energy of the ship, and the fender reaction force should be less than that of the ship's side. Allowable face pressure of the board. The calculation formula for effective collision energy when a ship is berthing is:
E = MVn2 / 2
In the formula:
E is the effective collision energy when the ship is berthing; M is the mass of the ship, calculated based on the full-load displacement; Vn is the normal speed of the ship at berthing.
If it is set to 0.7, at this time: when the normal berthing speed of the 25,000 t ship is taken as / s, its effective impact energy is; when the normal berthing speed of the 50,000 t ship is taken as / s, its effective impact energy is Is; when the ship's berthing normal speed is taken as / s, its effective impact energy is. After testing, the high reaction force cylindrical fender satisfies the condition that the energy absorbed during the shrinkage deformation is greater than the effective impact energy of the ship. At this time, the shrinkage deformation of the fender reaches about 48%.
The energy absorption of the drum fender is: the normal berthing speed value of a ship of 50,000 t is / s, and the normal berthing speed value of a ship of 25,000 t is / s; from the perspective of energy absorption by the fender, the hull The front 1/3 ~ 1/4 hit the fender. When the ship berthing at the drum-type dock fender, the normal speed within the berthing angle must be such as.
The energy absorption of the cylindrical dock fender is the normal berthing speed value of a ship of 25,000 tons / s. When a 25,000 t ship is berthing at a cylindrical fender, it must have a normal speed within the berthing angle.
When a 25,000 t ship berths at a cylindrical dock fender, it must be within the berthing angle. D-type and arch fenders, as secondary fenders, do not accept the impact force of the ship. Its role is to prevent the ship from drumming The dock fenders contract to a certain level and come into contact with the upper edge of the dock, so the characteristics of these two fenders cannot be used to define the berthing speed and angle of the ship.
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